I never bothered to watch the 2nd. The first one was cool enough to keep me interested. Sometimes I have to channel my eight year old self to really get into these movies, but it's entertaining to say the least to watch these Marvel comics come to life now.
I'm actually going back to watch a lot of the Marvel movies that I've missed the past few years. When I read the good reviews for Avengers, I figured that I needed to go back and play catch up. From what I understand, here's the order that they go in:
Movie - Seen it?
Iron Man - [X]
Incredible Hulk - [X]
Iron Man 2 - [ ]
Thor - [ ]
Captain America - [ ]
Avengers - [ ]
I saw the new Spider-Man movie, and it was good, but it's not in that same arc.
I've heard good things about Iron Man 3 as well, so I might as well consider that movie list above as the list leading to IM3