I'm going to judge this one against Iron Man, Thor, and Captain America rather than Avengers or any of the sequels. This movie has the task of being a good origin story for a team of superheroes and a good stand alone movie. That could be very hard to achieve. Hitting that balance is hard enough with one character, let alone a group. That said, Marvel has done a very good job with their movies, so I have high hopes.
I was skeptical at first from the initial articles. But, the previews make it look like a really fun movie that does not take itself too seriously. I just hope that they have a good soundtrack like in the previews.
The previews are convincing me to watch... I guess that is their intended effect... It really looks like it could be a fun movie, not very serious but fun action and adventure.