I think the first one was such a big hit because not many people was expecting it to be one particularly. Iron Man isn't (or rather wasn't) and A list hero until the movie and that coupled with RDJ's general awesomeness was a winning combination.
I have to agree the trailer wasn't especially fantastic (War Machine aside *squee*) but I don't think the first movie's trailer was particulary good either, so I'll wait and see =3. Most comic book number 2 movies are usually better than the first (Spidey, X-men, Blade, Hulk sorta, Fantastic Four), it's just the threequels you need to watch for =P.
I'm not particularly excited about any of the ones you mentioned Jayme. I mean I wanna see them all of course, but Thor isn't a character who particularly thrills me except as part of the Avengers, though I'm more interested in Thor than Captain America, who I think is a rather dull hero personally.
I just want them to be done so we get to see the Avengers =3