The characters are completely one dimensional. They have absolutely no substance whatsoever. We never learn their motivations, their hopes, dreams, fears, and desires. The closest thing to approach a character is Sigourney Weaver's, because we learn a little about her backstory and her life before the events of the movie. She has that recycled, tough-yet-still-feminine quality she had in Aliens. But she's not the main character, and this clearly wasn't an ensemble film. Something's wrong when the most interesting character in the movie has almost no screen time and is not the main character.

The plot makes absolutely no sense. They apparently require this guy to work an Avatar to penetrate the Navi society and somehow convince them to leave. And they ensure that he's going to be a success at this by outfitting him with human clothes and a gun, and not bothering to teach him the Navi language. The Navi also seem to be able to immediately tell that he's not a real Navi. So how the fuck was he supposed to penetrate their culture? they know about humans, and they know about the avatars, so how is this going to fool them? and who the hell is he supposed to be, anyway?

So even if you take into account that maybe the Navi will accept a human who looks like a Navi, even though the Navi know that they can't trust the humans because they clearly want to destroy the planet and harvest its riches, why is this even necessary in the first place? it doesn't seem like their plan was any more elaborate than "shoot the tree down and bulldoze the place".

So later, when they finally attack the Navi, they decide to go to the one place on the planet where they know that their technological superiority will not give them the upper hand. So why the fuck did they bother to engage them in battle? are you telling me that the entire unit that can survive on this harsh world, not one person bothered to say

"hey, maybe we shouldn't attack. Seeing as how they're not a threat to us, have never been a threat to us, and will never be a threat to us, why not just take what we want? they can't stop us, and if they attack us, we can just mow them down."

Then there's a bunch of minor plot niggles I had:

First we see that the humans are somewhat afraid of the natives because they fire poison tipped arrows. Then later we see the arrows bouncing harmlessly off the ships. Then we see the arrows firing through their windows.

Okay, this might be a bit of stretch, because it's a fantasy movie and all, but seriously... how can humans, even though they're occupying an avatar, possibly know/perceive/understand/control the neural interface that the Navi use? it's not as if the humans are actually physically occupying the body of the avatar; it's just a signal that comes from an interface with the host (which also brings up another point - if they can build interfaces like this that are so highly advanced, why do they still man battle suits that clearly have similar interfaces? i'd imagine in this scenario, cost wouldn't be so much of an issue, seeing as how it might take 5 years to get reinforcements). So how does this work? the human brain isn't equipped for such an interface because we don't have such an appendage. Again, bit of a stretch, but it still bothered me the whole movie.

I would agree partly with this, as in my review of the movie I thought Jake's backstory should have been developed more. However, I didn't find Grace the most interesting character at all; Neytiri was for me.

That's why Grace was so pissed off about Jake in the program. Originally, it was supposed to be Jake's twin brother that HAD all that training, hence them insulting him for being a dumb soldier at the beginning. I don't recall exactly, but I also don't think that he was supposed to be found by the Na'vi at that point in time. It just happened they were attacked and split up and Jake was saved by Neytiri and started interacting with them; also, it was the Norm character that knew how to speak the language and it seemed like he was the one that was supposed to try and integrate with them, hence his being pissed off later when Jake is the one staying with the tribe/clan.

Are you asking why it was necessary for the humans to try and integrate? Giovanni Ribisi's character explains this in the beginning, that ideally they don't want a war because of negative press, thus the attempts to do so diplomatically.

All they knew was that their instruments wouldn't work in flight. Given the Colonel's war mongering, I imagine he thought it would still be a pretty easy fight. I don't really understand your pseudo quote though; what do you mean take what they want? They couldn't because it was under their giganto tree.

Agreed, that was kind of silly although it looked like they were throwing larger weapons at the ships at the fight versus just smaller arrows earlier.

To be honest, I never think about these type of things so it doesn't bother me. I think these type of things are only a major issue when you happen to dislike the movie. There are just as many glaring plot holes in the Terminator movies that can be broken down similarly as far as Time Travel goes.