You're going to get the core fans, which is number X. Batman, Spider-Man, Superman, those guys get pretty large groups regardless, the marketing and actors sell the rest the opening week. From there it's all about how good the movie is (usually). If the movie sucks, people won't see it again.
So how important is it that Thor is a good movie? Very important, because when it's a sequel, which Avengers essentially is, people base part of that on a previous movie. Batman Begins and TIH suffered because of the movies before them. I think the Iron Man buzz is losing steam, people will still come to watch RDJ act cool like he does in virtually every other movie he's ever been in, Thor will probably have the least amount of core fans and the cast is a good acting cast for the most part but wont' draw, captain America is the opposite, full of beautiful people, not as many good actors. It's really a mixed bag but the importance of Thor being good, not necessarily successful, but a really good movie is highly important.
If Thor is generally well recieved, even if it doesn't sell a lot, it will help out tremendously because people will at least buy the DVD. I'm much more worried about Captain America because he's what people think of when they think Avengers. I think Thor will have great acting but honestly the pics I've seen look cheap, like a Sci Fi original. I REALLY hope with editing it looks better but I wasn't impressed with the effects of Wolfman but it worked because it was old school like Wolfman. To be successful with the mainstream audience you need good effects, some movies draw their entire fanbase off of effects regardless of how terrible the rest of the movie is.
