Long ago I spent a lot of time doing 3D presentations on computer screens and projection screens (and Colgate invested in a fairly-portable non-depolarizing projection screen in large part so that I could give 3D talks where I'd pass out polarized glasses, showing both slides with a pair of matched slide projectors and simple animations with a pair of 286 PCs where I synchronized the Turbo Pascal programs with 2400-baud serial port connection code); it's mildly amusing that I've seen Avatar twice, but not yet as 3D because my wife doesn't care for 3D glasses.
(Spoiler?) It's a profoundly silly movie, which I think is fun -- in part because I like to think, after watching a movie or sometimes after reading a book, about how I would fix it. For example, the central combat scenes are poorly motivated: we want the high-tech space-traveling bad guys to attack the Soul Tree of the low-tech aboriginal inhabitants and get ambushed, but we don't get a real reason why they should put troops on the ground or even in the air. After all, they ought to be able to send a missile to a known location, or hit it from a satellite. So why expose themselves? The answer could be that all high-altitude stuff (and missiles) are managed by Earth's Space Navy, which may be mildly corrupt and subject to restrictive rules of engagement; they are happy to provide satellite-based mapping data and they are unwilling to defend the good guys from the bad guys but they are not willing to let the bad guys use ICBMs or kinetic strikes. Easy...with obvious directions to go in from there. (This would add some consistency to the "bad press" remarks; if the Company controlled everything, there would be no press apart from press releases.)
To make star travel work, you need one of the backgrounds that make it work: a few years of cryo-suspension will not get a substantial ship from one stellar system to another without either a really major advance in physics, which we magically label "warp drive", or a civilization that can collect most of a star's output. Either of these would then involve some changes. Hmm. Borrow from the Honorverse, which may not always be coherent but does have a worked-out theory, sort of.
There are other things, which I won't go into here, but I will mention my hope that future movies in the franchise make full use of the fact that Eywa, a superhuman (planetary) intelligence who has presumably thousands or millions years of experience but never had a reason to develop the notion of science, has absorbed Grace's memories. Hmmmm.
update:Well, I'll add two others, just in case I come back and re-read this a few years hence.
- when I saw the bad guys approaching on the ground my first thought was, as mentioned above, "why would they do anything so silly?" but my second was "they can't possibly keep up with even very slow-moving fliers overhead." I've been in a jungle; you don't move fast. So I imagined jungle troop carriers for them. Start with a New York City bus, one that swivels in the middle so it can go around fairly tight corners. Now make it even longer but narrower and give it a bunch of swivel-points; one per passenger. Okay, it is now a snake, a series of pods, that could go between trees, but it still can't cope with ups and downs. That's solvable too: just look at the exoskeletons that some of the solders use, apparently brought over by Sigourney Weaver from the Aliens set. Put one of these in front; it can plausibly walk much faster than a human, without getting bitten by whatever's in the bushes. Fine, now each pod gets a set of robotic legs, with which it echoes the motions of the pod ahead of it (or of the lead exoskeleton, if it's the front pod). We now have a giant centipede which is fairly easy to generate with CGI and will look really cool and can drive through the jungle with soldiers inside, but is still possible for the Na'vi to ambush; if the fliers are going slowly, then having centipedes keep up with them won't look so ridiculous.
- The Na'vi are much larger than humans so their hunting arrows are a threat to the exoskeletons and fliers, but not much of one. I'd have them (or one of the "good" humans use a library of antique military equipment; I'm trying to remember if The various and ingenious machines of Agostino Ramelli (1588) has super-crossbows -- I think it does). So you come up with a simple crossbow that not even a Na'vi can cock by hand, but their horses (under direct neural control) can. One warrior on a horse, one on foot, two huge crossbows being passed back and forth, and you might be able to really damage an exoskeleton, a flier, the shuttle, or of course one of my centipedes.