I've seen the Avengers.
It was good.
I was under the impression it had already come out in the States, though.
here's my review, in short:
This movie is sort of simultaneously easy and difficult to review.
There's not terribly much I can say about it, but on the other hand, I don't really have to.
Here's the short version:
If you have seen if not all, but at least most, of the movies leading up to this, go see it. But you don't need me telling you that. If you are a fan of these characters, or just comic-book movies in general, you already knew what you wanted to do.
The biggest problem (that's simultaneously it's greatest advantage) is that it's not a stand-alone-movie. If you go in this without seeing the previous movies leading to it (Ironman-movies, Thor, Hulk, Captain America) you are not getting the whole experience. Characters and conflicts have been established in those movies, even if you'd be well versed in Marvel-comic-lore, you'd miss out on a lot.