I saw this at the IMAX in 3D and it was absolutely stunning. It didn't use cheap trickery like having things flying towards your face; instead it gave scenes extra depth. It was like I wasn't watching a sequence of images anymore; I was looking through a window at something really there. From the opening shot of the stasis pods, I was transfixed. And every time I took the effect for granted, another scene would show up with an even more impressive effect. I lost count of the number of times I said "wow" to myself over the course of the film.
I've seen 3D films before, but nothing full length and nothing quite on this scale.
3D is just a gimmick.
It's no more a gimmick than "high definition" is. It's just the next step up. It's a way to make films more enjoyable to watch. Obviously a bad film will be a bad film and 3D won't save it, but Avatar wasn't bad in the first place. It's very formulaic and borrows heavily from lots of other films, but it's a solid tale regardless, and the 'world' of Pandora is a believable and beautiful place. The attention to detail that has gone into the design of the creatures, the landscapes, everything, is incredible. I probably would watch it again in 2D, but it wouldn't be the same. The spectacle would be lessened. If you're going to watch this at home on a normal TV, you're probably going to wonder what all the fuss is about. It'd be like watching a YouTube footage of a rollercoaster ride, finding it underwhelming, and then thinking roller-coasters are underwhelming.
If 3D is a gimmick to get bums on seats, then consider it a success. I fully intend my bum to be on cinema seats in future if I can watch more films like this.