As I mentioned, I saw Captain America in preparation for going to see The Avengers. And a friend of mine and I made it out to an afternoon show of that, today.
I think I only found out about Joss Whedon's involvement yesterday, but I suspect that a lot of how well it worked can be traced to him.
And it worked very well, indeed. Plotwise, it was tightly coupled with both Thor and Captain America (with incidental connections to Iron Man and The Hulk). And the cast was very good; Robert Downey Jr continued his excellent work as Tony Stark, Chris Evans and Chris Hemsworth were solid in their reprises as Captain America and Thor, respectively. And Scarlett Johansson was even better in reprising The Black Widow. But the surprise, for me, was the fabulous job Mark Ruffalo did as Bruce Banner.
The banter between the various characters was quite good, and I especially liked the interaction between Downey's Stark and Ruffalo's Banner. But the friction between Captain America, Iron Man, Bruce Banner, and Thor was well-presented (might have been a little bit over the top right around the end of the second act, but was generally quite good). The only weakness among the characters was the relationship between The Black Widow and Hawkeye. They were the two characters who were supposed to know each other very well, and it just felt forced, for me. Both actors were good, otherwise, but there was just no chemistry there.
But that was a fairly small detail. As I said, most of the interactions were very good to excellent.
I'm not a big fan of The Hulk, but they mostly did a good job of working with him. They even got some humor in there, which doesn't happen often.
My biggest gripe with the movie was actually a technical one related to the 3D. Digital compositing has gotten to be seamless with 2D movies, but it finally hit me that some stuff that seemed a bit off was a failure of 3D digital compositing. It was especially noticeable in the fast-moving parts, and there were a lot of those.
I did think they missed one opportunity. Stark and Pepper were talking about the Stark Building early on, and Tony was giving her credit for 12% of it. When the fighting started, later, I thought they should have destroyed 88% of the building, and then had Pepper remark something along the lines of, "Looks like my part held together Tony. You've got to do a better job on the rest of it."
Overall, the story was good, and the characters went together well, so it was a very enjoyable movie. I'll be getting the blu-ray sometime soon after release.