The plot has been done dozens of times before and the story is extremely predictable, but that doesn't detract from what is otherwise a great film. In the tradition that Star Wars borrows heavily from traditional myths, so does Avatar borrow from current/historical events and many other films to create a satisfying film.
Beautiful voice acting and animation on every character and creature with the exception of Sigourney Weaver's Avatar which is just too uncanny-valley. Otherwise, exceptional work. You forget they aren't real at times. Protagonists were great, antagonists however were very flat.