So much to catch up on... I may forget some reactions I had, saw it a couple days ago, anyway, some other tangential stuff first:
At first I was like
Look, if you're expecting an original and compelling plot, you're in the wrong freaking genre. There really is no such thing as excellent literature or even a genuinely original, good, compelling plot in fantasy or sci-fci in any artistic format.
But then,
Orson Scott Card did a good job with this in the Ender's Game series (moreso in the later sequels, the first book was more stale).

(to be clear, imo Ender's Game was far, far better than the sequels. And on top of that out of all the possible examples of *good* sci-fi to use...) Though actually I was reminded of the aliens in the later Ender books by Avatar, due to the planet's ecosystem/sentience in trees/etc... (but see later in post)
Now, onto the magical cross-over match not exactly possible in our reality...though WeMade FOX still triumphs over Samsung Khan in this one, that angries up the blood...
So, I figure we're past the point for care over spoilers, so first, I've seen the film once and unfortunately it wasn't in 3D due to one too many friends who say they get headaches too bad. However, the graphics were still great, and I'm sure 3D was good, so that wasn't a problem for me with the movie. As others have surmised and said themselves, it was the plot that this movie really struggles with. I have to say it wasn't original at all - though it is almost comical how many
different other books/movies/television shows people have said had similar plots. I would go with the blockbusters everyone knows - Dances with Wolves and Pocahantas, as being the obvious ones that Avatar is extremely like. Some other comments on this:
-Those of you going on about SMAC/the hivemind concept - you should know SMAC wasn't the first either, especially Cheezy who should already know about Solaris. But in short, I agree - been there, done that, and better
-Other than the aforementioned Night Elf vs. Terran spectacle, the Vietnam movie tropes were way over the top. This is obviously where people see the references to Iraq/beat-you-over-the-head moralizing (and I agree that's what Cameron was up to using specific terms like "Shock and Awe"). But similarities to, say, Apocalypse Now are very clear.
-Arwon wins with the best reference of all in my view. Mostly because it's another reminder of why I really need to read more of LeGuin's work (I haven't read that one) but from what I briefly read about the book it sounds good.
But enough with the references/other similar works - so for my opinion on whether I liked it... I have to say not really, the plot was way to unoriginal, predictable, and annoying at times. This ties into the various failures at being good science fiction - part of it may have been expectations going into the movie, though, since A) I didn't know that much about it, and as some reviewer I read put it the movie really should be viewed more as fantasy/epic-storytelling and B) Avatar really is EXACTLY like Dances with Wolves. I mean, I had heard that, but I wasn't expecting it so, so much. So I have to second some other opinions here and elsewhere, namely problems like:
-bland or very uninspired characters - many weren't well defined as characters at all - "shaman native" or "science guy" and all. Then, of course, you have the complete mess of why the humans are so one-dimensional and supposed to be straight "evil" - the whole "mercenaries" thing is really rather contrived, same with the human's "racism." Flat characterization leads to unexplained/irrational leaps in the plot - like all of a sudden locking up Jake/the scientists even though they'd agreed to let them try diplomacy, the random pilot who turns sides (then gets killed, actually that + Grace dying were kinda darker than the rest looking back)
-The science fiction. I am also with many of you annoyed at unobtainium- what it does, what's really vital, the floating mountains, etc... The evolution (design? - that's a decent point at least that could be reasonable) of the organisms on Pandora clearly required a little open-mindedness too, and it would have been cool to really have non-basic humanoid aliens. But this would be forgiven if the movie didn't have to have those excruciating minutes of Hollywood Action TM where "techonology is teh suxxors." And of course little background on the humans/Earth - though it really seems any sequel would be an absolute destruction/genocide of the natives, with the implications of the humans being desperate to leave Earth/colonize elsewhere+the unobtainium. Overall, when we got to the climactic conflicts, I have to say Avatar succeeded at something very few movies have ever done for me - I was literally rooting for the bad guys. Archimonde actually destroys the World Tree, sure, if the movie had ended there on a sad note with "humans bad, imperialism bad" and all it would be manageable. But worse, the film did something I've experienced even more rarely - it had a chance to have a truly amazing ending, and abandoned it for the trivial. I think I've referred to this as something like the "Fountainhead ending" before (Spoiler - in this Ayn Rand novel, which is really too awful to be worth reading, the conclusion of the book still could have been more inspiring/heart-lifting, and insteads ends with the bitter protagonist giving essentially an eff you to the world). So, in the midst of the battle I almost thought that Cameron would exceed what I thought he was capable of (not forgetting
Titanic, that is)
It seemed that Jake's absolutely stupid strategy
really would fail- that he'd rallied the many clans of natives to a slaughter/defeat far greater than just the one being kicked out of their homeland. Which, unfortunately, parallels events which did happen in real Earth history too and so while very sad this would also have been unexpectedly profound for a Hollywood film. Instead, well, you know how it goes - despite a strategy where no matter the Na'Vi did from the onset, they still were mere seconds from their most sacred tree "ancestral/hive mind uplink" being destroyed, the power of plot pulls through. So, there's the obvious plot holes around the incredibly stupid human redshirt army - a planned bombing run nevertheless at very slow speeds and low altitude for a long time with rather useless escorts, from a space-capable military force, with a random ground assault leaving their base of operations undefended. And of course the magic failures of instruments, incredibly high natural armor of random Pandora beasts against cannons/machine gun fire (I

'd at the one firebat

). It basically came down to this - when it was just the Colonel with his knife-wielding mech I was still hoping he would kill the main character/female Na'Vi, then that even with the Colonel dead, Jake would still suffocate/be poisoned (of course, though, the actual ending was obvious at that point). In short, I can't point to exactly one specific bad element of characterization/plot/background that led me to root for the obvious villain over the obvious protagonist, but overall I was just annoyed too much.
-Other people's hype. OK, I know it's not entirely fair to hate on something for this, like Tim Tebow when a large part of the problem really is random journalist/sportscasters who are like infatuated children. But Avatar has this in spades - I can't stand hearing people not understand a movie, maybe references/similarities to other movies are forgiveable but the people who don't even get the themes that Cameron/the film were going for...ugh. And then there's the talk of major Oscars and all that - Avatar isn't even the best sci-fi film this year,
District 9 has it beat hands down.
tl;dr (I'm guessing very likely...though I won't rule out the one guy who finds a mid-paragraph sentence to quote and challenge me on, it's the way of the Internet).
First and foremost, Avatar is an incredibly pretty film that certainly shows what all that money on graphics and computer technology can do. I'm really happy to just see what's possible and know furthermore that future movies/videogames/etc... will continue to improve as the technology improves. And I'd say, despite all I've just said, it's worth seeing because it's so pretty. Just be very, very clear on what you're (not) expecting from the plot (If you've read this far/anyone else's posts you probably already know anyway). I probably would have enjoyed it more knowing what to ignore/not worry about - and if I see it in 3D now I might still seek a way to just tune out the dialogue/annoying story and just catch the pretty details. Also, I'd love to see some real science fiction series done justice with such beautiful graphics...How about a final and definitive remake of the
real spacefarer turned Kwisatz Haderach