I'm going to start of saying that this movie is a milestone in visual graphics, it is stunning and beautiful as well as impressive. The VFX team and the animators deserve everything coming from this point on.
That is where it ends though. Cameron really wanted this movie to be 180+ minutes. The entire story could have been told in 120. It's obvious there's an extra hour or so of scenes just there to show the pretty visuals. The story is outdrawn and there are scenes that could have been completely left out and be told by short clips. The slaughter of all the animals is one of those scenes and a scene I'd rather not have seen.
Another thing is when they killed the whale and said this stops human aging and is the only reason why we are on this planet...What?!! What about Unobtanium. Or did you really forget that is the only reason why you are on the planet.. Or to terraform and kill all the natives was another reason thrown out there. But its like Cameron completely forgot about Unobtanium, and so did all the humans.
And by the end of the movie we are exactly where we started. Humans are still on pandora, nothing was solved, nothing was resolved.
Then there's the whole accent going on among the Sully kids, it's "bro" this and "bro" that, in almost every sentence to a point where it becomes outright annoying to listen to their conversations and lose all interest in the characters, their story and what happens to them.
Same goes with Neytiri and her screams and breaths, it sounds like she's had a cold that she never recovered from. I understand that's how the actress sound, but they could have fixed it somehow.
Visually stunning with a story and characters that are easily forgotten. I walked out of the cinema not really caring when the next movie will be released.