So far, the best movies leading up to the Avengers have been Iron Man, and Thor, and it seems rather a strange coincidence that both of them feature rich guys who need to be brought down to earth (In one case literally). Not that this is a bad thing. Tales of men who learn to seek redemption can be compelling tales. However, given that we've received two of them in the Avengers series it's refreshing to come across a hero who doesn't need redemption. All he needs is a chance to prove he's a hero.
Captain America is the tale of an underdog superhero, my favorite kind. Steve Rogers just wants to show what he's made of, and he does. Of course it's not as easy as that, even when he gets his inevitable transformation. Some want to keep him in a lab somewhere and others want to make a show of him and his abilities to sell War Bonds. Of course he chooses the latter at first, because he's at least doing something, but when he sees a chance to really help out, he leaps on it. I won't tell you how that turns out. (Note: The 'selling War Bonds' segment has the best reference to the original costume I've seen in a Marvel movie.)
Once he starts really serving his country, and actually fighting, it's great for him, though not what he expected. I won't spoil what happens, but suffice to say that sometimes when we get what we want, there are things we didn't want that come along with it. He sees the darker side of war, and it makes a nice conflict for the final stretch of the film, even as he devoutly serves his country.
Hugo Weaving makes a good villain as always (though not as good as his turn as Agent Smith from the first Matrix), and Chris Evans does well as a weak Brooklyn boy turned super soldier. The rest of the cast is great, especially Tommy Lee Jones as Colonel Chester Phillips, probably the most entertaining character in the movie.
In short, Captain America is a different kind of superhero, and that's a good thing. And underdog fighting in World War II isn't usual material for such movies, but it works well. In this writer's opinion, Captain America is the best movie in the Avengers line yet.
This makes me more than excited for the actual Avengers Movie. Bring it on!