Just got back from an East Coast showing at midnight. Theatre was pretty well-populated....anyone arriving 10 minutes prior to showtime would probably have been stuck sitting alone or sitting in the first few rows. Why do I always feel sorry for these people?

I think the problem with the super generic story is the same problem that King Kong had -- the ending is such a forgone conclusion that length becomes a consideration. Oftentimes it feels like you are tapping your foot waiting for things to come to a head. This wouldn't be a problem though if the characters were empathetic or interesting, but they are mostly just flat. If I were going to see the movie again it would almost certainly be for the last 20 minutes, which would make all the stuff that comes before it even more difficult to sit through. The Na'vi are never really humanized and their society never really explored....if the prelude had to be so long, it would have be nice to get a sequence like the Hobbiton part in Fellowship of the Ring - some section where we see more about how they live and play. They are just stoic mystics and hunters....more like Tolkein's stuffy joyless Elves than the Hobbits.
I was much more impressed with all the CG than I thought I would be, and much less impressed by the 3D. The 3D didn't seem any better or worse than other stuff I have seen in 3D, though I suppose there is less of that pop-up-book effect. A lot of times you cease to notice it at all.....I wasn't sure if my glasses stopped working at times. I had a headache through the last 45 minutes of the film, though I am still not sure if it was due to the glasses that pinch your head like a pair of tweezers or the 3D itself. I wouldn't say I felt particularly immersed, and there are still plenty of shots of stuff coming at the camera (though less obvious and gimmicky). A lot of the problems I had with RealD continue to exist with IMAX 3D.....things can look kinda flickery, or sometimes hazy and semi-translucent (like when you hold your hand about 5 inches from your face and it looks as if you can see through it).
CG looks very good, though I'd still say it mostly looks like CG whenever there is anything other than an inanimate object on screen. To WETA's credit though, there are still of shots of that look like humans in prosthetics rather than CG furries. Mostly I think this is a step forward in animation and getting the movements down right.
If you live in the boonies and can't get to a 3D theatre, I wouldn't sweat it too much. The 3D isn't a gimmick, but it isn't really what makes the film. The technology still has a long way to go, especially if it's going to hike ticket prices by 50%.
I dunno how the movie will play with normal audiences. My friend is a pretty average moviegoer and he liked it, but certainly wasn't wild about it. He said military/human scenes were on par with "that shitty videogame that Mark Hamill was in with the giant tigers"

But he really enjoyed all the Pandora stuff. He said Sigourney Weaver was terrible - I merely thought she was phoning it in. I feel like they could have gotten somebody much better and much more into it.
Overall I'd say it was just okay -- mostly worth seeing just to have something to talk about with everyone else. And I'm hoping it will bring us out the "Shrek"-era of CG films and towards something a little more serious. It doesn't feel like a game-changer or a leap forward or whatever, but it is hard to hate if you take it on its own merits and not the hype. I'd rank it below almost all of Cameron's other films....maybe better than The Terminator (my least favorite).