I saw it twice and I preferred it in 2D *gasp*
Only reason I saw it twice is because I went with two different people; the second time 'round I stopped paying attention halfway through because it just bored me.
The story was predictable, but it was solid; the world of Pandora was beautiful but it didn't strike me as utterly amazing. Something about a bazillion gigantic fluorescent plants took me out of the world =/
The lack of maturity at some points got me too; in the big climatic fight scene, I didn't get a huge impact of what happened because there was no lasting effect. Generic soldiers disappeared without a trace; no blood or even a look at their bodies after their job of dying was done. The only characters that ever bled (I'm so focused on the blood because it added visual impact; it showed quite physically that these characters were injured or dead) were the mains. Maybe that made us focus on them more and sympathize with them, but it sort of told me that this was a kid's movie as well... Which isn't such a bad thing, except that it suffered for it.
It sort of let me down too; District 9 was a so much better movie.