Forget what I said about Star Wars: I broadened that statement a lot. And in the grand scheme of things, no Vader being Luke's father isn't one of the "greatest plot twists of all time." Star Wars cherry picks pretty much everything it has from Greek and other classical mythology; nothing is, or ever was, innovative about it's core plot.
[quote name='RedvsBlue']While I agree that predictability shouldn't be a determining factor in whether or not its a solid story, originality is and Avatar is far from original. Dances with Wolves, The Last Samurai, District 9, etc. Its a story we've seen a hundred times and Avatar did little to expand upon the story or re-invent it.[/QUOTE]
Originality is not required, either. You're ignoring creativity (which is wholly different from originality), which Avatar has in spades.
Avatar is not really original or unpredictable. It is, however, incredibly creative. The setting is extremely imaginative and creative, solidly built and fleshed-out, and the plot is effectively told. Thus: solid overall story.