You have to keep in mind that Captain America has always been the scary comic to adapt. While most comics purport to be morality plays at some level, most modern ones are fairly down to earth about it. But Cap is the exception: bone-deep sincerity is the absolute core of the character, and that's hard to portray. So I was pleased to see the character played just right, starting with a Steve Rogers who absolutely *hungers* to be able to do the right thing for the right reasons, and who manages to keep that after he's turned into the brawny hero. (Not trying to mess with his WWII origins helped: you can get away with ignoring modern irony in a period piece.)
Mind, this is not a film to go to for historical accuracy. Indeed, they made the curious decision to mostly decouple the story from the Nazis per se, by reinventing Hydra as a sort of rebellious Nazi science division and putting the Red Skull in charge of that. So there's nary a swastika in sight -- instead, Hydra heads are everywhere. OTOH, the story is almost painfully realistic in a few ways -- in particular, Cap's first "missions" (which I shan't spoil) ring rather horribly and comically true to real-world politics, probably the best small tweak that the movie makes to continuity.
The movie is replete with shout-outs to Marvel fans, who will find tons of subtle visual in-jokes throughout -- from the first shot of Arnim Zola, to the Human Torch's tube showing up in the background of the Exposition. They do a nice job with this, rarely shoving it in your face, so the fans can have fun with it while not being annoying to the people who are just here to see the movie. As with most of the Marvel movies, they don't worry about sticking strictly to canon so much as keeping the theme and style of the comic intact, and they succeed completely.
They do manage to include a raft of significant WWII characters, with the notable exception of Nick Fury himself. (The rest of the Howlers do appear, as fairly major characters.) Peggy Carter, the original Agent 13, is a major character, and besides being an ideal love interest for Steve she is an absolutely *delightful* character herself: smart, gutsy and generally dangerous.
(And it suddenly occurs to me that I didn't see Stan Lee anywhere. Anybody able to tell me where he showed up? I assume he's in there somewhere.)
As a movie, it's a good romp; as I'd expected from the trailers, it has a rather Indiana Jones flavor -- an idealistic hero, cacklingly evil villains, terrible (and slightly supernatural) devices and of course a plot to Take Over The World. Note that there is a good deal of typical comic-book/war-movie violence, so it's probably not ideal for small children.
Overall, one of the better movies of the summer. I'd say that X-Men: First Class was a slightly *better* movie, but this one is the most *fun* so far. Don't go in expecting a lot of depth, but it's a fine film otherwise...