I thought both movies were very good (despite the critical reception of Green Hornet.) Short version: Green Hornet is awesome with humor and Captain America is awesome with a good story.
The Green Hornet:
If anyone remembers anything about the old Green Hornet show, its that they hired an Asian martial arts expert (Bruce Lee) to play Kato and a boring white guy (who knows? who cares?) to play Green Hornet. The lingering racism of the times meant that Bruce Lee couldn't be the star, but because of his martial arts skills he ended up doing all the heroic stuff, while Green Hornet just sat around. (And in fact often ended up being the one who needed rescuing.)
The producers of the movie dealt with this in the best way possible, by making it a comedy. Kato is a genius engineer and a great martial artist. The Green Hornet is the playboy son of a newspaper magnate with the skills of... uh, having lots of money and thinking that being a superhero would be cool?
The belief that since it's his idea then he must be the hero and Kato must be the sidekick is presented as "only" an "innocent" spoiled upper-class sense of entitlement, rather than just racism or a purposeful and spiteful attempt to deny Kato any credit. But purposeful or not the fact that he controls the editing process at the biggest paper in town means that all the stories are about.. the Green Hornet, of course.
And unlike the original, at least to the best of my knowledge, Kato starts getting (quite justifiably) resentful about this state of affairs fairly early on. However the inter-personal conflict is handled in a mostly humorous way, and the villain is also very humorous in an "unintentional" manner that to me calls back to favorites like Without a Clue and Undercover Blues. (However those are kind of my go-to for movies that are funny but not dumb, so they kind of get compared to everything =)
The action scenes mostly go for "awesome", though they have the occasional bits of humor thrown in as well, especially when the Green Hornet gets involved. shelleycat thought they were a little disjointed at points but other than the obvious (and by this point kind of expected) uses of bullet time and stop/spin type effects i didn't notice anything like that.
I admit to not knowing much about Captain America, but he's never seemed very interesting to me. The idea of an American SuperSoldier(tm) who is Patriotic and Fights Nazis! always seemed a bit cliche to me and possibly even jingoistic, so i just never bothered looking into it. However without spoiling things to much, i can say that they did a pretty good job of not playing up the patriotism/jingoism aspect too much.
Steve Rogers/Captain America really didn't have much of a character arc as far as personality goes, but that was a very deliberate choice. A lot of the other superhero movies lately have been about jerk-asses who either naturally have superpowers or practically have superpowers fall into their laps, and then have to struggle with themselves to learn how to act like a hero. Captain America is about someone who already knows how to behave like a hero, but lacks first the ability and then the opportunity to actually be one. That could be viewed as boring, but after the umpty-umpth "I'm a jerkface whose heart of gold will eventually be revealed" it's kind of a refreshing change of pace.
Character development aside, the plot itself had a good set of arcs (there's got to be a better way to say that) and told a pretty good story and everything followed a pretty natural progression. The only bit i'm not sure if i agree with was the five minute or so opening scene. I wonder if it might have been better if it had been moved elsewhere in the movie.
There are definitely a couple threads that were left hanging loose, not in the "they forgot about it" kind of way, but in the "life doesn't always wrap things up tidily" kind of way. Some of that may be because they plan to deal with it in "The Avengers" sequel next year, and some of it just might never be resolved.
On a broader note, there were three new "big name" superhero movies coming out this year. Thor, Green Lantern, and Captain America. One of those concepts seemed interesting to me. One of those concepts was one i knew a far bit about, for someone who'd never read any of the comics at least. Guess which one ended up sucking? Apparently the relative depth and theoretical value of the backstory involved doesn't matter in these things, it only matters if the movie is being made by Marvel or DC.
Since Marvel started their own independent film studio they've made five movies. I never watched "The Incredible Hulk" because "Hulk" kinda sucked, but apparently the newer one is actually a reboot and got decent but not great reviews. The other four movies have all been outstanding as far as superhero movies go, and have actually been pretty darn good just considered as regular movies. DC still farms their movies out to whoever, and still gets very mixed results. Even the preeminent Superman and Batman series have had their occasional duds.
Does Marvel have some secret formula to making good movies? Or is this something that any company could do if they just put the effort into it? Which of course then brings up the question, well why don't they do that?
But as far as the Marvel movies for just this summer go, if someone were going to choose between seeing Thor or Captain America i'd probably say that Thor is more fun but Captain America has a better plot. Of course that's not a comparison that's going to be especially relevant until they're both out on DVD, at which point i'd say go ahead and rent/Netflix/whatever them both :)