An absolutely stunning visual feast; Cameron was given the technology (and budget) to create a breathtaking world that you have to see.
The film has several overtly political moments (i.e., thinly veiled references to preemptive war & Iraq) that soured things for me and many in the audience--there were audible groans when some of the dialogue came up. These side rants run the risk of depriving the movie of ‘timeless’ status.
However, setting that aside, it is STILL a must see. I don't care if you're a genre fan or just a general moviegoer: see this movie. It is a remarkable experience and presages--I think--the arrival of a whole new class of movies in 3-D--it feels like we've finally 'arrived' at this new generation of cinema!