We absolutely loved it - went to see it without the kids first, so that we could decide. Pandora is a breathtakingly beautiful planet, and the animation is simply incredible. This really stands out in the scenes where there is mixed CGI/live action, and will amaze you in the scenes where there are real humans interacting with Na'vi.
The role models are fantastic - a disabled hero who won't let anything get in the way of living a full, meaningful life. He fights for what he believes in with all his heart. Many teenage boys will really relate to Jake Scully, and his character goes through a gripping development in the film. All of the female characters are strong and inspiring, whether intellectually, like Grace, or militarily, like Trudy, and the female Na'vi are very much the same - they're feminine, but they work on an equal level with the men in every way.
There is a fairly large amount of violence, although it's not very gory, between the humans and the Na'vi aliens. However I felt this was well-balanced in showing the horrors of war - the colonel is shown as a ridiculous, dangerous character and violence is never glorified. In fact, when Neytiri loses one of her family in battle, she mourns him at length and weeps over his body - it's desperately touching but probably too upsetting for under-12s or so.
Purely because of the lengthy battle scenes, the complex plot, and the fact that overall the film is pushing for 3 hours once you include trailers and such, I really wouldn't recommend this for under-10s at all.