I had a couple of calls from people seeking legal advice before Avatar was released. I told them all I no longer litigate (true), but the last thing I wanted to be involved in was something as silly as this law suit which has been filed. The book has never been published and sounds like what my friends in publishing call a "Mary Sue." I'm sure that if the manuscript ever hit a slush pile, it would be used in a late-night, read-out-loud session at a science fiction convention, which is what happens to really bad manuscripts.
There are legitimate cases where work has been stolen and the plaintiff prevails. The Northern Exposure case won by Glen Kulik always comes to mind. And Harlan Ellison had a famous run-in with James Cameron over Terminator (Cameron made an admission against interest which led to it, I hear. It was years before Harlan was my client.) Harlan also went up against Paramount over a short-lived TV series called Brillo, which I hear led to a billboard near Paramount for a while (again, before he was my client.)
I once had someone from Eastern Europe call me to say that a disaster movie had been stolen from him. His English was not good enough for me to believe that had happened. Actually, several times I've gotten inquiries about what would be a theft of idea case where I didn't think the caller had the language skills to have written a screenplay or novel that anyone would have (a) read or (b) stolen. (If this sounds a little elitist or arrogant, I'm married to a very successful writer and wordsmith--an "old god" of his field--and I have spent time with many, many famous writers. I also spent time working in publishing. I know the difference between good and god-awful.)
Most of the time, the plaintiff is working on a theft of idea theory--somehow their idea or work got into the hands of someone who then used it as the basis of a movie. The plaintiff would not have given it away without expectation of payment. These claims of quasi-contract only have a chance of working in California. It's a claim under state law, and most states won't recognize it.
Copyright does not protect ideas, only expression. If a substantial amount of the "idea" has been expressed in writing--an outline, a treatment, or a draft of a screenplay--the first thing a studio which is hit with a theft of idea case will try to do is kick it from state court to Federal Court as a copyright claim. If the plaintiff hasn't registered the copyright to the work, it puts them behind the eight ball at the start and severely limits plaintiff's damages.
The next step in the plaintiff's case is going to be to show access and substantial similarity between plaintiff's work and the alleged infringing work. And defendants don't get off the hook by showing how much they changed from the original. There is no magic percentage of change that makes it original, no matter what you have heard.
Access such as having a meeting with the producer who produced the infringing work and submission of plaintiff's work is pretty darned good potential access (which is why most places won't even look at work that's submitted cold without getting a waiver from the writer.) The similarity becomes the big hurtle. There are experts who do detailed analysis and charts to present evidence of similarity or lack thereof.
In a science fiction or fantasy work, traveling to a new world with strange new creatures is endemic to the genre. There are hundreds of tropes in these genres. Space ships, winged aliens, elongated, aliens of different colors, military invasions, mining (even Star Wars had a mining planet) etc., etc., etc. The stranger in a strange land concept goes back to the Bible and probably beyond (the phrase comes from the Bible.) Using any or all of these concepts doesn't get you to copyright infringement. Things have to be a lot more specific and it is even better if chucks of dialogue are identical (and not just because that's what anyone would say under certain circumstances.)
I haven't seen Avatar, which is strange considering my background. But I'm not a Cameron fan and, while I think this lawsuit is bogus, there are plenty of other sources from which Cameron probably stole his ideas. But he's allowed to steal the ideas, just not the expression. Even people who are as turned off by his poor dialogue as I am say it is the visuals that make the film and he did a great job with them.
Among the material I've seen people cite as source material for Avatar's plot and other elements are Dances with Wolves, Pocahontas and Ursula K. LeGuin's Earthsea stories. When I finally get around to watching it, I may have some suggestions to add.
I expect that this lawsuit is going to get thrown out at the motion stage. With a bit of luck, the judge may even sanction the law firm if this is as frivolous as it looks at first glance. I'm having a hard time reading the complaint without laughing.