Okay, let's try to make this flow somewhat coherently.
Obligatory disclaimer: I LOVE the Inheritance Cycle. As a kid it was nearly the only thing I read. Over the years I continue to reread it and each time I'll spot a new plot hole or inconsistency that I didn't notice when I was younger, but it doesn't mean I love it any less. You can still love something while acknowledging its flaws.
Secondary disclaimer: I am not a big fan of Brandon Sanderson's stories. However, I firmly stand by his First Law of Magic, and the difference between soft and hard magic. I only really get invested in fantasy that has a hard magic system. It's why I loved the world of Eragon as a kid so much more than other fantasy, because other than the occasional inconsistency it has a hard magic system that makes sense.
I guess I'll start with the broader story as a whole, then break it down to characters and then the nitpicky detail stuff after that.
The Story:
Overall the idea of the story is very appealing and I still like it. Outside of Alagaesia there is a Cthulhu-esque cult that worships an ancient giant monster sleeping underground. This monster sends out subtle mental influences that give people dreams and visions (the more I think about this the more it really does sound like Cthulhu). It's less generic than the "good heroes vs. evil tyrant" that the original series has. I like that. One problem: this doesn't take center stage until about 45% into the story. Up to that point it's a side quest to get a little bit of vague information. The proverbial "long walk for a short drink of water".
I say that because all of these side objectives don't even earn him information that is directly related to the main story. Murtagh goes through a scale heist that involves him use special magic that is so cleverly uninteresting and only goes to show that sometimes Murtagh can be clever with the way he uses spells.
Then there is the Moby Dick portion of the book that takes far too long and is also relatively uninteresting. (The only things of interest regarding the fishing trip was the fact that Murtagh really isn't trained very well in magic. I was screaming at him to stop trying to use a ball of fire as a source of light when underwater, but later we learn that he really doesn't know enough of the Ancient Language to do anything else. The second is that Murtagh actually felt some kinship to the Empire's soldiers, which I do think is interesting and I'll come back to).
After the Moby Dick section we then move to another heist. He earns gainful employment and uses it to get access to the special vault. Admittedly, going through the rooms of the vault were kind of interesting because of the strange artifacts, and he was clever with draining the door crystal of energy to power the wards. Well done Murtagh. Overall the heist was interesting enough, but was ultimately a let down because when he returns to Carabel he is given the information all of this was for: and it's barely anything new. Even the abduction of Silna by Wren might not even be related to the Dreamers at all. So now we're 45% of the way into the book and have only learned something that could have been discovered/found in a very simple way to leave room for more character development.
Next, he goes to Nal Gorgoth. He starts off his visit as a quasi-undercover mission, planning to get the information he wants through playing the game of customs and court etiquette. Okay, I guess. Unfortunately, this doesn't contain anything very exciting other than discovering a brooch and going on a royal boar hunt where he gets trampled into unconsciousness. And Bachel shook the mountain (which is the point that I figured out everything that was going on, making the mystery much less interesting). That's not enough interesting things to justify taking up 20% of the book.
Next we get 15% of endless torture, trauma, and slavery, which does nothing for the characters because they just escaped a life of torture, trauma, and slavery. Not only is it relatively uninteresting, it goes on way too long.
Then the last 10% is Murtagh spelunking with monsters while Thorn destroys a town. There are weird monsters in the caves. Why? Doesn't matter. Is it important? No. Did it make the story any more interesting? Not really. Finally Murtagh gets to the final boss. They fight. He wins. He is rescued. Flown halfway across the continent while unconscious, wakes up in a nice city already healed (Frodo, is that you?). Nasuada (but no kiss, boo). Roll credits.
Yes, my percentages only go up to 90% because on my reader the last 10% is the glossary and acknowledgements and I forgot to take that into consideration.
So, the cult/kaiju monster aspect is interesting and cool with greater implications, but it was twice as long as it needed to be with too many side missions that didn't contribute enough to the story to justify their existence. However, I am happily awaiting the next book because I am curious to see where the story goes. One misstep does not ruin the series and I do really like Paolini as an author.
The Characters (worth mentioning, it's not a lot):
Bachel: I'll start with her because I have the least to say. She's fine. I wouldn't really want to hear her life story to make her a sympathetic villain so I'm fine with that being left out. She's just a wide-eyed religious zealot and did a good job of it. Next.
Uvek: My man. Uvek is cool. Shaman. Lives alone. Best friend was a bird. When his new blood brother accidentally cuts off his horn he says, "No problem bro, it'll grow back and I'm not trying to get laid so I don't care if it makes me ugly. Let's go find someone else to kill." I like him. Next.
Thorn: Oh boy, this is tough. I LOVE the angle of his claustrophobia. It's nice to see his PTSD being addressed and manifesting in a way that has real consequences. It was done beautifully. *chef's kiss* Now, my issue with Thorn is that I feel like he is still a stranger to me. I wanted more of him in Inheritance, and was excited for him to be the main dragon of the new book. Unfortunately, it seemed like there kept being new ways to put him on the back burner. Whenever Murtagh was in towns he had to hide outside somewhere, usually too far for them to communicate regularly. Then in Nal Gorgoth he was there but again they talked very little. Then none at all during the drugged and tortured section. Then Murtagh was underground and couldn't talk to him. I don't feel like I got to know him at all besides his claustrophobia. I don't have a good grasp on his personality. (His somewhat arrogant attitude is normal for all dragons so that doesn't count).
Murtagh: The titular clumsy hero. His arc is... something. I kept thinking his decisions were odd and was trying to justify them by claiming his trauma gave him insecurities that were driving him, or other such deeper explanations. It wasn't until about 75% of the way through that I realized all of my attempts to explain his behavior was just headcanon, and the truth was that there was really only one reason for most of the decisions he made: plot. I could go on for an hour about him, but it would be way too much. This whole book had the stench of a story where the author would think of a scene he thought was cool, so then would try to force his characters to arrive at that situation, even if it didn't really make sense for them. I did appreciate seeing more of Murtagh's time with Galbatorix, both before his escape and when he returned and Thorn hatched for him. Also, I did enjoy seeing him long for the comradery he felt with the Empire's army. For one, it actually humanized the Empire's army in a way they hadn't before. Eragon slaughtered them by the thousands like they were faceless stormtroopers, but even just a few short lines in this book did remind us that they were just normal people too, most of them conscripted against their will. And it's nice to know that Murtagh actually did interact with them in their downtime, instead of him just being a brooding loner that always slept on a hill away from the camp. I like to think that after a battle he would walk among the men and help heal them the way that Eragon did with the Varden. Perhaps showing them some kindness because he understood their plight of being enslaved to do the King's bidding. I also liked Murtagh being sassy about Eragon. Also, I did like finding out that Galbatorix really didn't train him well at all. After the original series I was under the impression that he would be fluent in the ancient language and probably even some other unique magic Galbatorix learned and shared with him that Eragon never learned. But no, Galbatorix taught him the basics and juiced him up with some Eldunari steroids and sent him to fight Eragon. This forced him to be more clever with his spells which I liked, but that was also kind of ruined because of the inconsistency. By the end of the story I didn't really feel like he was any different than the character he was at the beginning, or even who he was at the end of Inheritance. His character wasn't ruined by any stretch, there's still room to do interesting things with him in the future, but I don't feel like much was done with him here, in his own book.
The Magic:
I'm not really even sure where to begin with this one. It felt like so many things were different. Not expanded upon, just different. The first thing that stood out to me was something that seemed to completely contradict what Brom said in his first lesson with Eragon, and the thing that shapes the rules of magic: the law of equivalent energy (as I'm calling it). After Murtagh catches his fish that seems to change size each time it's described (Also, why would Durza want to make such an intricately indestructible monster fish? Why not something cooler? Why a sea monster at all?), he needs to deliver the head to Wren as a job resume. From the outskirts of town, he wraps the fish head in a cloak and decides that it's so heavy that if he dragged it all the way to town he would be exhausted by the time he got there. So instead he uses magic to transport it there. Really? Wouldn't you be just as exhausted because of the energy rule? Now, I've seen people saying that it took less energy because he only used magic to lift it a little to avoid the friction of dragging it on the ground, so it was easier. Is that any different than slinging it over his shoulder though? But whatever, fineeee, I'll grant you your little loophole. But it's such an insignificant thing, so why would Paolini include this scene that needs outside explanation to avoid being a broken magic rule for something that amounts to nothing. Why are we spending time describing how Murtagh chooses to get a fish head to town without getting tired instead of devoting that time to something important?? So much unnecessary filler.
Then there's Murtagh's own loopholes. I like the idea of him having to find clever ways to use magic because of his limited knowledge of the Ancient Language, and I've seen some people even compare it to coding the way he sort of includes if/then statements in his spells (which seems like it should only be possible with extensive knowledge of the language, but whatever, it's still cool). The problem is that getting tricky with his spells means that it kind of steps over existing precedent.
The bird skull amulets. Sometimes when someone wears them it's as if it makes them entirely immune to spells. Murtagh will cast a spell at them and not feel any energy drain, as if it didn't even trigger a ward. Then other times, it's as if the amulet is just where a ward is stored, and is immune to being deactivated by the Name. No explanation of why the amulets have different results and behave differently at different times.
During Eragon's training with Oromis, we learned how important it is to word spells as a process, so that they can be abandoned if the completion of the spell would require so much energy that the caster would die. Does anyone remember that? I'm not sure Paolini does. Because in this book it seems that someone can cast a spell and if it seems like it will be too much energy they can just cut it off. I don't think this is a problem in itself, but it goes against what we have learned before. It's not always a complete refutation of previously established rules, but we often just gloss over them as if it isn't a problem and it makes magic seem so much more loose and easier and less dangerous to use. In older books we're told a few of the Forsworn died because they weren't careful with their magic use and accidentally killed themselves, but there doesn't seem to be any danger at all for Murtagh to be casting all kinds of spells at people despite not knowing their strength because he can just cancel the spell, even if it's not worded as a process. Murtagh knew Bachel had the power to literally shake the mountains, yet he was still casting non-process spells at her not knowing what wards she had. I think going by the rules of previous books that would have killed him.
Poor Brom. Brom died because Eragon didn't know the Ancient Language enough to properly heal his wounds (why didn't you have wards Brom???). "Waise heill" was only enough to heal the surface damage, but couldn't mend his internal bleeding and damage. Then in Ellesmera Eragon learned the language and how to heal more significant wounds with more complex spells. He even comments that with what he learned he could have saved Brom easily. Alas, it was not to be. But Murtagh? Murtagh could probably reattach someone's head with those two simple words. Why? No one knows. People will say "it's not just the words, it's the intent" but I call BS on that. Eragon had the intent to fully heal Brom. Elven spellcasters have the intent and anatomical knowledge to heal with simple worded spells, but they can't. They have to use longer more specific spells to heal different types of damage separately. Murtagh's a bad boy though, he doesn't play by the rules.
Enchanted objects. Another incredible method of healing is the special Urgal healing rock. I don't have an issue with enchanted objects in general, but it only makes sense that they would have to be really specific. Also, they need a specific energy source. The amulets? I figure they're programmed to take energy from whoever is wearing it. The Urgal stone? It can apparently store its own energy, even though we've clearly established only special crystals can store energy. But Murtagh transfers energy from the crystal to the rock, and then touching it can heal everything from punctured lungs to drug induced mental confusion. Why not? Just go with it. And although it wasn't confirmed to be true, Murtagh guessed that Nasuada is enchanting all of her currency to avoid getting dirty or tarnished. What?? First of all, why? Second of all, how? Where do the coins get the energy to stay clean? Arya's grass ship drew power from plants and life around/under it, so do the coins do that? If you work at a bank do you get tired faster because the coins are stealing your life force so they can stay clean?? I know this is weirdly nitpicky but if something is going to confuse the rules, just leave it out! Especially if it isn't even important. Who cares if Nasuada's coins get dirty?? It was such an unnecessary inclusion.
Mentioning Bachel again and how she shook the mountain. She was drawing energy directly from Azlagur, right? That's how I guessed there was a giant monster underground because how else would she get the energy for that? Murtagh even wonders the same thing. So if she has access to the energy of this kaiju, why doesn't she use it to power her wards? That seems straightforward enough. But her wards seem to only be tied to her own strength. That's convenient for Murtagh.
Not directly magic, but related to it: vorgethan. This has changed drastically since the previous books. In the original series it was basically a drug that just made the person so drunk out of their mind that they couldn't even remember any words in the Ancient Language (but still retained other memories/faculties). In this book, it serves as a really effective drug that completely cuts a person off from anything magical (magic, telepathy, energy transfer) without messing with their mind (and this actually makes much more sense than how it was in the first book). Murtagh says that his mental confusion only came from Bachel's fog she blew in his face, not the vorgethan. The vorgethan is apparently even stable enough that magicians in the kingdom microdose it unless they register with the magic police. Clearly this was a massive change. Why? Because plot.
Continued in comments...