I took my 8 year old son to see Avatar tonight, wasn't quite sold out but very full. We were able to see the 3D version, and it was INCREDIBLE, visually. Well worth the extra buck or two for the 3D experience. It's not gimmicky, but just gives everything some subtle depth throughout the whole flick.
The storyline is pretty similar to Dances With Wolves, but it's not distractingly bad, as I'd worried, too. Sam Worthington, Zoe Saldana, Sigourney Weaver, and Giovanni Ribisi all do fine with their roles, as does the guy who plays the head of the military force.
If anyone's on the fence about this one, it's worth it for the visuals alone - the planet (Pandora) is incredibly detailed, and it's like you've been dumped into a Roger Dean album cover.