Avatar is an amazing technical and aesthetic achievement. It's like looking at the world's most beautiful matte painting.
I don't actually think there's three hours of movie in there. Many scenes seem to have been inserted just to have an excuse for characters to walk around in a bioluminescent wonderland. But that's okay, since the alien landscape looks really, really cool. I didn't find the plot that interesting, and the only parts I perked up for were the bits that involved things borrowed from Aliens. And the occasional weird plot hole.
One thing I thought was awesome was that Sigourney Weaver smokes, but is not an evil character. It seems like it's been a few years since that's happened in a movie. And the smoking was an irrelevant character detail, possibly just thrown in to give her something to do with her hands. I don't smoke myself, but I'm getting kind of tired of the Only Evil Characters Smoke thing.''
Incidentally, whenever I see Michelle Rodriguez in a movie, I'm reminded of Janette Goldstein's portrayal of Vasquez in Aliens. So it was fun to see her basically playing Vasquez in a James Cameron movie.
Oh, the plot holes. I'll give you three: Michelle Rodriguez probably should have been court-martialled, I think it's weird that Jake's security level (which you can see on the video log) never changes, and the Colonel mentioned that they're in low gravity but I don't think they actually are.
Anyway, it's a remarkable achievement and quite pretty. And I like the idea of making a movie you want to see in 3-D in a good movie theater, because it's a nice end-run around Internet movie piracy. I just wish I liked the movie more. Also, it seems weird that it costs a quarter of a bullion dollars to make a movie with no sets. Shouldn't that make it cheaper?