WARNING: This contains spoilers. Read the book first if you care about that.
As a huge fan of the character Illidan from the Warcraft universe, I was excited to get my hands on this book and read it. Was it worth it? NO.
This book, to put it simply, has some of the worst pacing, POV switching, and direction I have ever seen in a novel published under a recognizable franchise. I get that it's based off a video game series, but this is no excuse for its lackluster style and numerous flaws.
Perhaps the most glaring problem with the book itself is the title. A book called Illidan should have some strong emphasis on its titular character, but he is not as strong a focus as you would think. A better title would be something like Before the Fall so we wouldn't be mislead into thinking that Illidan is the main POV and focus of the story. It's so misleading because a good chunk of the book actually takes place in the POV of this author's original character, a Demon Hunter named Vandel.
Vandel is, what I assume to be, an anchor for players to follow, especially those interested in Demon Hunter class lore. Some of the better written parts of the book are when Vandel changes into a Demon Hunter. King goes into some intense and gory details of the process which I appreciate. However, rather than use a preexisting Demon Hunter lore character like Altruis the Sufferer, Varedis Felsoul, or even Leotheras the Blind, we are instead meant to sympathize and focus on an OC that adds absolutely nothing to the original story presented in the games. Demon Hunters characters fans of the games WOULD recognize are simply name-dropped and not given the proper fleshing out that would be appropriate for this kind of novel. To add salt on the wound, King loves his OC so much that he ends the novel in Vandel's POV. VANDEL'S? Are you serious, Mr. King? This hilarious Gary Stu is so bad that King even ends the book with Vandel disappearing into the night. Vandel is so utterly useless in the grand scheme of things that he gets demoted to just being a scout in the plot that's continued in the game. When you hype a character this much only for them to be a throwaway in the main story canon, you know you've made a really bad character. I find it rather hilarious too that he has him face off with Maiev one-on-one, gets his skull cleaved by her blade, and still manage to live and walk away like it wasn't such a big deal. Did he leech off something to heal like a Demon Hunter in-game and in-lore would do? NOPE. Well done, Mr. King. You didn't reach Med'an levels of bad, but this is still pretty bad regardless.
Other characters in liege with Illidan are also pretty glossed over and not fleshed out. This includes his Blood Elf council. Hell, King cares so little about them that near the end of the book when Illidan is preparing the portal to Mardum, the pacing goes from them talking to Illidan to being dead by the next paragraph. There is no big battle or anything to show what the hell happened, only that they were slaughtered.
Now while I make it seem that King completely ruined the characters, this is actually not entirely the case. I was actually engrossed by the parts where Maiev and Akama conversed because it fleshed them out as characters, and these are interactions we do not see in the games. King also does a rather fair job at showing Illidan's inner weaknesses such as how he refuses to outwardly express vulnerability so that he can maintain a mask of strength to command his followers. This works with his character and does add to the overall character of Illidan fans of the series would already know.
Unfortunately, the awful pacing and POV switching really hampers the story. There are giant leaps in the time from one event to another, and in many cases King resorts to simply telling us what happened rather than showing the events unfold. This method of storytelling is so bad that I physically couldn't will myself to continue the book for weeks on end. I found roleplayers on the game's infamous Moon Guard server to be much more compelling storytellers. The poor pacing and POV switching are especially evident in the big final battle at the end of the book. He spends around ten pages on the Illidan battle but hardly anything on the other aspects of the fight. For example, one unfamiliar with the games would have no idea who the Aldors or Scryers are, and if someone gets into the games after reading the books, they will be surprised to see how much William King completely glossed over. Events of Warcraft III to the Burning Crusade SHOULD have been deeply fleshed out in Illidan's POV and expanded on, but alas, King missed this opportunity.
I haven't read any of William King's other works, but the style he uses in this book is really aggravating to read. King uses the pluperfect a LOT in his sentences, leading to a lot of missed instances where he could have resorted to active verbs instead to make the scenes much more compelling. He also tends to go into third person limited way too often RIGHT after a POV switch. This is especially evident near the end of the book with the battle of Maiev and Vandel. It's an action sequence–we don't need to know their thoughts after what just happened! It's just completely unnecessary and breaks the tension of the scene.
With all that said, is the book worth reading? If you're a fan of Illidan and Demon Hunters, then I would say it's worth checking out just to say you read it. Vandel's experiences prior to him becoming a Gary Stu and seemingly one of Illidan's favorites are really useful for crafting the background of a Demon Hunter roleplay character. Some of the parts King did expand on, like the whole siege of Nathreza, are also useless for people interested in the lore, and as mentioned previously, the exposure of Illidan's inner weaknesses helps to make him a more sympathetic antihero. However, I would say you can pretty much gain all this knowledge by simply reading up on the important details in the Wiki pages rather than slog through this mess of a book just to get the important bits. I really can't recommend it unless you're prepared for a book that missed a perfect opportunity to flesh out more aspects of the stories and characters the games already introduced to us. I will admit such a feat would likely have resulted in more than one volume, but I would have preferred that over this single volume disaster.