He bothered me a lot too. I think that the actor did a fine job, I feel like it was the script's fault. Cripes, not even a cliched "The Na'vi killed my son!" subplot? I'm being tongue in cheek here, but something would've been nice. Why was he such an asshole?I liked the movie, more than I expected to even. The story was engaging enough, though I have a few major issues in the area of character motivation. The one thing that I absolutely loathed about the movie was the main villain. I'm not sure how it all went so wrong, whether the acting or the writing was more to blame, but the character as presented was such a snarling, over-the-top cartoon stereotype that he ruined nearly every scene that featured him. Unfortunately, his scenes accounted for a large chunk of the running time.
Considering he received his scars his very first day on the planet, and he hadn't left since, his motivation was pretty obvious to me: he wanted to dominate this two-bit moon, whatever it took. Pandora hurt him, and he was apparently content to spend the rest of his life hurting it back. He'd been waiting for a long time (decades?) to get his chance to really cut loose, and he finally got it. That Sully sided with the Na'vi and the forest just made matters worse. The planet was his enemy. I'll admit the dude's motivation is completely insane, but then you'd probably have to be to have his job.
I had similiar issues with Michelle Rodriguez's character, why did she defect? I know her and Sully were buddies, but did they even have more than one scene together? A few motivating story beats for more of the supporting characters would've helped the movie a lot in my opinion.
It wasn't just her and Sully, I got the impression she was friendly with the scientist camp. She ferried them around at least a few times, and probably spent a lot of time with them. I think it would have been more believable had a few more pilots refused to attack innocent people, though.