Spectacular visuals is about the only reason I go to the theater anymore. They've got to be combined with a decent movie that I'm otherwise interested in of course, but I'd rather just watch most other movies at home.
A movie needs more than just plot to score amazingly high marks in my books. In some movies, the action and visuals greatly add to the artist appeal.
I'll probably see Avatar in the theater, but despite all the good press, it's still not pulling me with the force of a "must see" flick.