I avoided reading this until I saw the movie.....which I just got back from tonight.
First, I have to say it. GREAT summer popcorn flick. I don't go to these kinds of movies for "deeper meaning," I go for a Friday night fling to escape reality for a few hours, and that's exactly what I got. I'm what you call an armchair comic book fan, in that I love a lot of these characters but I deliberately don't go comic book shopping (for fear of gaining a new addiction, mostly). So I know them peripherally, and I've seen all the individual movies leading up to this.
Overall I'd say they did a fair job covering the characters. This one had a LOT more humor than most of the others, and had the audience laughing through the film. Interestingly, my wife didn't think Captain America was the eye candy; her favorite was Tony Stark every time. Personally I'll pick the Black Widow scenes. Scarlett Johansson in tight black leather?? Yes, please.
If you ask me I'd say the Hulk was one of the best played parts in the film. I loved his character, and
almost felt bad for Loki in that pivotal Hulk/Loki scene. Almost.
Sip, I agree that Thor wasn't quite as well written in this movie as he was in his own film, but I think it's just the way the cards fell. There were a LOT of characters to cover here, and sometimes one or two take secondary places to move the story forward. You see that a lot in Star Trek films, too.
Oh, and before y'all ask me MY age, I'm 187 years old and still have most of my own hair.