Always when a movie project involving superheroes is released there's concern about how they will look on the silver screen. I remember some complains when the first pictures of Captain America and Thor showed up. There was the danger of they looking silly or campy, but in the end I think they ended up looking great and believable (for a superhero that is).
Now with Avengers I haven't heard such comments and I think we can all agree that they all look amazing! Even the villain Loki which has over-the-top costumes looks kick ass. And Hulk why CGI never looked more likeable and the effects were not fake or distracting.
I think that besides delivering the goods, Josh Whedon showed that superheroes can be done right on movies and have set a new standard for this kind of films.
captcha: doctor who? (!)
Personally, I thought all of them looked fantastic, hulk and Iron Man look very believable.
I liked that they stuck with it for Captain America - he was designed to look garishly patriotic, and they carried it off well. Thor as well, somehow they made ceremonial armour look like it belonged on a battlefield!