I also saw Avatar in 3D, and I have to say that I loved it. Sure, the basic story had been told before and had cliche moments, but I don't think its ever been told this grand. Jim still knows how to make epics. The 3D was subtle for the most part, and while I want to see it again, I'm not sure I could watch it in 2D the same way. I'm not sure if they can take 2D films and make them 3D, I'd have to see it before I make a judgment on that, but I think that movies of this caliber should be made in 3D to start with.
I wrote a review on my blog, if anyone's interested.