Finally watched this.
I enjoyed it, but I don't feel it came together until 45 minutes in, once the team was assembled. I found some of the bickering forced and draggy, but I really loved the (not sexual) tension between Stark and Steve, and the banter between Tony and Bruce. I'm also dying to know what happened in Budapest!
But I didn't care for ....Loki. I rooted for him after Thor, but here, he just seemed too one-note. And to the end of my days, I'll proclaim this: Tony Stark would NEVER build a butt-ugly skyscaper like that. From his homes to his IM suit, he's all about sleek, stylish, futuristic (if slightly retro in feel) modernity. He would NEVER build that tacky eyesore of a building!!! Ugh! Whoever thought that up should be shot.
I also thought the movie could have done without the whole "Agent Coulson has a girlfriend" bit. I understand why it was done, but he's been in all (or nearly all) the lead-in, so the girlfriend bit just seemed like extra sentimental schmuck for the sake of wringing up emotion. (His being a Captain America fanboy DID seem appropriate though and not gooey and fitting to the professional agent who regales all the Avengers together.)