Beautiful imagery will only take you so far. The film follows the "Titanic" timeline in setting up the characters and location to draw the audience in before applying the EVENT - in Titanic it was the iceberg, in Avatar it is the mercs attack on the Na-vi aliens.
Unfortunately, that EVENT took too long to get to and I found myself wondering how much longer I had to sit there before the story arc came about.
Avatar is definitely worth seeing in the theater in 3-D, but I can't give it 5 stars due to it focusing more on location development than character development and running a bit long on time.