"Two-dimensional characters in 3D" should have been the tagline. The story is one we've all seen before and doesn't add anything new into the mix. The characters are rigid archetypes that don't seem to grow or develop in any way, except for the hero, who changes all the time.
Technically however the movie is stunning. The 3D is beautiful and masterfully handled by Cameron. We even get a few great performances from actors in supporting roles. Giovanni Ribisi and Stephen Lang do a lot with very little.
I'd recommend seeing it if only to show that 3D can be a cohesive part of a film instead of just an added gimmick to sell more expensive tickets.