I think the script went too far with Tony Stark being narcissistic; that aspect was a little nauseating. I liked the interplay of the other characters; I'm not a comic book fan so I didn't know they had names like Black Widow, etc. There was just enough fantasy to signal it was a comic book come to life, though; the fight scene Natasha did was a great example. ..and great camera work.
Loved the one-liners. I think every character was perfectly cast. I just hope they scale back on the narcissism for Tony Stark and add more scenes that show his brilliance and cerebral wit; nobody does that better then RDJ.
Overall, the first IM was better than 2; but 2 is still a must-see.