Holy fleeping crap.
We saw it in 2D. I literally cannot imagine how 3D could possibly have made it better, because every single second was dripping with so much awesome there was no room for any more.
Watch the Avengers. If you like comic books. If you don't like comic books. If you liked/disliked/haven't seen either of the Iron Man movies, Thor, Captain America or anything else Marvel Universe related. If you like/dislike/don't care about/don't recognize the name Joss Whedon. It doesn't matter. See the Avengers.
If you understand the concept of 'movie', see the Avengers. If you are a fan of anything at all, see the Avengers. If you are breathing and have any earthly means of watching this movie, see the Avengers.
If you have seen it, see it again. Stay past the end of the end credits in case you didn't previous times watching. I want to watch it again, right now. I may need to watch it again later this week, if I can figure out a way.
Holy crap this movie. I need to watch it on repeat for a week with a notebook and a pause button to process all the glory. I don't know when the DVD comes out but it needs to be right the hell now.
So, yeah, I kind of recommend it.