Oh and....it legit caused depression in people due to Pandora being fake and not real. I think at the time there was a lawsuit that was thrown out that some people wanted to sue him for creating such a great world that couldn't be enjoyed in real life.
http://www.cnn.com/2010/SHOWBIZ/Movies/01/11/avatar.movie.blues/index.html
I remember hearing about this at the time and thought it was bullshit. No, we don't have glowing plants (well... we do, but not to that level) or floating mountains, but we do have some pretty freaking awesome natural beauty in this world. I can almost guarantee you that the people "suffering" from this spent virtually all of their free time watching screens instead of actually getting outside.
Yeah I've always been perplexed when people mention how imaginative Pandora is when it's pretty much majority Earth with some CGI elements. Perhaps my bar is too high but it felt like a decent idea but ultimately weak effort at an alien planet, at least as far as the reaction to it.
This is exactly why I love the movie though. Cameron was drawing up this world for decades. Not only is it pretty, but it obeys all the rules. Every single plant we see, every creature, every tool, structure, or article of clothing we see was meticulously designed. Not just in appearance, but in function and within the rules of physics and evolution as we know them. The size of Pandora and its gravity is why the fauna looks as it does and the creatures are the size they are. The monstrous leaves and home trees weren't in there because they were convenient, but rather that's what we'd see in those conditions. The build and coloring of the Na'vi is based on their environment and they look exactly how they should given the variables around them. We'll see a lot of this with the water tribe in the new film - differences in appearance due adapting in a water-heavy environment vs the forest.
I could type up an argument for everything we saw in the first film, but I'd be here all weekend. Cameron brought a properly imagined world to life.
For example, when I saw the film the first time, Jake walked by this thing. I thought to myself "how are they making light?". Well, Cameron thought of that (and every other minute detail of the world). Per the survival guide that was released, it's the bladder or other internal organ from an animal. They coat the inside with a nectar like substance (probably what the direhorses were eating in the first film), let it attract glowing insects, and then the Na'vi would sew it shut. Boom. Natural street lamp.
The Helicoradian acts like a venus fly trap. It collapses in on itself when something lands on/in it.
I could go on and on. I mean, clearly concepts from Earth were borrowed, but if you consider his imagination coming from an evolutionary standpoint, rather than just a lifting of stuff on Earth, a great appreciation is to be had. I think. Cameron imagined a world to a sickening level detail. Far, far beyond anything else I've ever seen in both film and videogames. Everything in his world fits. Nothing is out of place or breaks the rules for the sake of being in the movie.