I went ahead and watched Avatar in IMax. The visuals were nice. The story was pretty stupid. I found the alien world pretty dumb too. Plants that light up when you step on them? Plugging in to various species with your braided hair? Does their hair unbraid?
The 3d did add to the movie and didn't seem gimmicky to me. I watched it because I felt I had to for the sense of history, and I feel it was worth it despite the horrifically bad writing/story.
Actually those things already occur in nature here on Earth, just in different environments than shown in Avatar, so they make a great deal of sense scientifically. The largest paradox is the floating mountains, as anti-gravity is, (as we understand at our present state of development), completely impossible and counter to all laws of planetary physics, (black hole environment may be an exception, but that's only far-fetched theory at this point). The movie was science fiction, and very good sci-fi at that, with no more outrageous ideas than Star Wars, Star Trek, Aliens, or most other good science fiction. If you're not into sci-fi, then chances are it's not going to appeal to you. But even for those who don't care for sci-fi, the special effects applications are beyond anything ever attempted before, and can be appreciated in that manner, if no other.