Okay I saw Avatar in IMAX 3D... can't be a better way to see it. I almost got afraid of heights.
In short: a marvelous experience. A very credible world and Na'vi characters, amazingly clear in storytelling the complex science stuff (how the Avatar works etc), amazingly well made world, a true movie experience of the likes I've not seen in a long time (ago in a galaxy with only the OT). Very well thought through visual themes (the use of avatars-mind links to animals-mechanical avatars (i.e. the robots they drive ..... the death of his brother leads to a new life for Sully, who also ends up in a box to get a new life in his Avatar, to ending getting a real new life and several more.... kudo's Cameron)
Downsides: the very very one dimensional bad guys (yes Cameron, you sure disappointed me there - why the heck can you think of all kinds of plants and animals and not think of a bad guy in the caliber range of what you had in The Abyss... just to point out that you do KNOW how to do that) and the rather predictive last 45 minutes or so.
Nevertheless, it was enjoyable all the way and I recommend everyone to watch it, preferably in IMAX 3D. I wonder now how it'll hold up on Blu Ray.
One more thing that I can't wrap my head around: why do they use these Avatars at all, since the Na'vi know they're not real Na'vi but Sky People in disguise? Can't they do their scientific work as humans by now???