I really liked the forest, the Na'vi, the Avatars, the flying. Lots of visual pleasure. If that's what you're looking for (and who isn't?), you probably want to see it in 3D IMAX.
I wasn't disappointed by the predictable plot or characterizations - I expected that. No problem there.
It was the bombardment by noise and violence that was the spoiler. It's not just offensive - it's boring like most violent action films (yes, there are exceptions). Battle starts - story stops.
Unobtainium. Turns out it's not a cheesy term coined by filmmakers, but an actual scientific term. Unobtainium is the term used by scientists to describe an unknown or impossible to get substance. Who'd o' thought?