I'd read in articles prior to seeing Avengers that there would not be any one 'main' character, but I was dubious, considering Iron Man's reputation as a scene stealer. However, Avengers was actually about ALL of the team, and focused well on each of them in turn. There were great witty Joss Whedon one-liners (he's a great writer), and I thought there was a good balance of strength and vulnerability. I'm definately hooked!
(Just a lil comment, I saw it in a packed theatre, and it was really great how everyone started clapping when Stan Lee made his appearance. He must be a very happy man.)