Just came from a Real 3d version of the movie. Surprisingly I left without much of a headache, at least much less than from UP.
This is a movie you have to judge in 2 ways: As a basic movie containing a plot, actors, and script, and from a technical level. Avatar scores conversely equal on both fronts.
As a basic movie it is rather lacking. The story is cliche, the acting is rather campy, there's very little blurring of characters (they're either totally bad or totally good) and seeing humans portrayed as the bad guys isn't exactly a feel good story. Oh, and not to get political, but the movie definitely does take a very liberal stance on things. And to comment on what the previous poster said, no the movie does NOT bash US Marines. If anything, they'd have to be considered mercenaries or part of a PMC.
On a technical level, the movie is astounding. It looks like James has finally figured out how to make CGI not look like CGI. The aliens look like humans covered in paint (as opposed to something in a PS3 game,) the planet looks astounding, and human ships and computer technology actually look like something that would be used in the future.
So overall, yes this is a movie worth seeing, really because of amazing technological feat that it is. Of course, if you don't care about such things and want a good story and performances that move you, you're better off going to a family reunion.