Fantastic movie, great technology, incredible vision by Cameron to create this new world from whole cloth. Very Tolkein-ish in that way.
Saw it in 3-D at an IMAX. First 3-D movie for me and it's a pretty good technology. Still has limitations - you can't tilt your head way to one side or you'll screw up the lens polarization.
Anywho - this is a film that will become a groundbreaking classic. It's going to become a standard, a must see for anyone who likes movies.
The very basic theme of the movie is not new, but the setting, the concept of living vicariously through an Avatar are presented in such tremendous detail that you really believe it all - you buy in.
Go see this in IMAX 3D if possible, or just regular 3D.