As always, here be spoilers.
I asked for Marvel: 1602 for my birthday last year, knowing only the hook: Marvel-verse heroes in Elizabethan England, instead of the present day. Also Neil Gaiman. Knowing Gaiman, I expected the layered, beautiful, intelligent story, but I didn't expect it to be integrated into the modern-day Marvel canon. I thought it would be much more of a fanfic/what-if situation.
The story starts by establishing characters, setting, and the threat that must be stopped, and as the book goes on we meet more characters and get further twists. It's a great all-round read, with requisite superhero power usage and intrigue that kept me flipping pages, but one of the things I liked best was turning a page and going, "Hey, it's that guy! I know that guy!" followed by either "Of course that's what he'd be doing" or "That was an interesting career switch. Huh. Wonder why?"* I really liked how Gaiman wove so many of the Marvel standbys into the story and made it seem right, and how well he made the characters fit into the time period. How well some of the characters fit without needing to be changed.
If you've been following this superhero project of mine, you probably know that I mainly know the Marvel-verse from the movies and internet-fed geek osmosis. This still means that I know the basic situations the characters find themselves in, I know some of the relationships the characters have to each other, I know how the characters relate to their world. (I think. Hopefully.) So it was interesting to see all that being rewritten and how Gaiman handles all the origin stories in a world where technological explanations won't fly. Of course he'd use magic and/or the arcane and instead, because what are superpowers but magic anyway? Plus Elizabethans had a healthy belief in magic already, or some of them did if John Dee is anything to go by. Using magic grounds the characters in their new world.
Gaiman handles the impact of superpowers on seventeenth-century Europe very well all round, but I'd expect nothing less. I'm thinking mostly about the Inquisition going after the witchbreed here, and the fear James I instills in just about everyone with powers. It felt very believable to me while I was reading and, I'll admit, generated more of a sense of wonder than the Spider-Man omnibus did. That was straight-up action. This is shiny, with an open-ended feel not only because not all the Marvel characters appeared in 1602 but also because in the end, the characters have the whole future ahead of them. Anything could happen!
When I said the superpowers in 1602 were caused by magic, I actually lied. The characters approach the powers as having magical origins and the way the powers are described reinforces the idea, but they actually result from the universe trying to reset the Earth after one Steve Rogers is thrown back in time. Therefore, the superpowers are caused by quantum, as Terry Pratchett would say. Which is essentially magic anyway, due to Clarke's Third Law and most people not understanding higher physics. And of course, the introduction of future!Captain America means that Marvel: 1602 isn't just a rewriting, it's a parallel universe.
To sum up: Marvel: 1602 is pitch-perfect on characterization, setting, and story, and hits every note I didn't know I wanted from a reworking of the Marvel canon. There are hidden levels you can peal the story apart to find, and more going on than you actually get to see on the page. And I desperately want a sequel, or prequel, or something to I can see more of everyone's adventures. (Alas, I will probably not get it, even if I somehow manage to buy/inherit Marvel.) I could probably reread the book and pick up on things I didn't catch the first time round, and that's always a sign of quality fiction for me. I wholeheartedly recommend you read this, if you're anywhere near the "target audience" of comic fans, alternate history fans, and Gaiman nerds.
* There were also "oh!" moments pertaining to people's powers, people's relationships, and what America means.