All that coalesced into a true cinematic experience, and its why it made nearly 2.8 BILLION dollars at the Box office. Movies are not always supposed to have some sort of deep message or engrossing story, they are first and foremost supposed to be entertainment, and that's what Avatar was, pure entertainment. For tens of millions of more people than the Hurt locker was I might add. The hurt locker was, for the most part, not entertaining, and carried no real deep message, it was basically trying to one-up Jarhead, which was head over heals a better film, yet didn't win best picture.
Cameron actually started writing Avatar in middle school, he even showed the binder full of line paper he wrote all his ideas and scripts on during an interview a while back. He wanted to start making it before he even finished Titanic, but he realized he needed to wait until special effects had matured enough for the film not to look dated and crappy a year later.