While I thoroughly enjoyed this collection, the major problem is one I expected: It's incredibly dated. Most comics from this era are, and this was no exception. In fact, the only exception I can think of off the top of my head is "The Amazing Spider-Man," the majority of which still works. "Tales to Astonish," which feature the adventures of Ant-Man and the Wasp, are cheesy, but have fun with it in a way a lot of the poorly-aged comics don't.
The beginning of Lee and Kirby's "Fantastic Four" does have fun with the cheesiness, sure, but there is also an air, at times, of seriousness, and it doesn't mesh particularly well when a page before there was something absolutely ludicrous. The Marvel Universe was in its early stages here, and it shows; one big positive is that the comics continuously get better as they go on, as the universe that we all know and love takes shape.
The characters are the real stand-outs here, even when some of the stories are lackluster. Ben Grimm, the Thing, shines with personality, and while Mister Fantastic may seem a generic scientist character at first, his strengths and flaws shine through as the book goes on. The Human Torch, in the beginning, comes off as nothing more than a hot-tempered (no pun intended) teenager that works slightly worse than Spidey does, but he does grow as a character, albeit more slowly than the others. Sue Storm is great when she gets a moment to shine, but those occasions aren't nearly frequent enough. Doctor Doom and Namor the Sub-Mariner are two amazing villains, and Alicia Masters (the Thing's girlfriend) is a character that, for whatever reason, I have always loved.
There are some poor characters, and I would be remiss not to mention them: The Puppet Master is a mediocre for at best, and I didn't love Miracle Man, either. Add the likes of Kurrgo, the Impossible Man, the Red Ghost, and the Mad Thinker and you almost have as many forgettable villains as you do interesting ones. Luckily, Doom and the Sub-Mariner more than make up for the infrequent appearances of the aforementioned antagonists.
This is a collection of stories that made comics--not just the ones in the Marvel Universe--what they are today. To a certain extent, it's like comicbook history, and I do recommend it. It's important to keep in mind, though, that not every aspect of it has aged for the best.