Since I'm sure everyone here has gone out to see this film, or are going to very soon, it's definitely worthy of a discussion thread.
I recently saw it again, and it's better than I initially thought. The writing is not only solid, but it's exceptional, especially when considering what Joseph Campbell had to say about modern myths (I implore everyone to check out The Power of Myth). Lucas really dropped the ball with the Star Wars prequels, but James Cameron has picked that ball up and knocked it out of the park. Cameron is clearly the better student of the master.
I hear people talk about how the effects carry the film, but it's the story that's turning this film into such a huge hit. It's going to cross 1 billion in ticket sales worldwide in a matter of days (on its way to surely beating Titanic's record). After a screening of the film, my mother-in-law even asked "so where were the effects?" She thought it was all real! Being someone who has worked extensively in 3D animation, I was absolutely stunned to see what they were able to pull off in this film, but I also realize that most people don't quite notice it, since they are being taken in with the events of the story. The real magic isn't in the effects or the technology, but in the emotional catharsis being provided by the familiar, well-told tale. And the (insane amount of) technology is really working to service the story without overshadowing it.
Anyway, I highly recommend everyone go see this film while in theaters. You're really missing out if you skip this major event.