The Marvel films are good for what they are. None of them are terrible. Ironman is pretty solid. Probably the best of the lot.
They're not really comparable to Batman. Accept that they deal with super heroes. The Batman series was levels above.
As for Avengers, I thought it was the best "summer blockbuster" in a long time. But that's not saying much. The competition is what, transformers?
I went opening night and fan reaction was insane. Cinematically, it's fine, the director did a solid job of pulling the stories together and the acting was capable. A lot of crowd I saw the film with are probably life-long Marvel fans and they love it. So for that, it's a winner.