3D has been a big failure so far, because you have to shoot the film for the median, and in order to do that, you have to understand that median. James Cameron did a great job of shooting Avatar for 3D. It was more of a compliment to the film, not a stupid gimmic to sell more tickets. Although, ironically, that was Cameron's foresight to push Avatar into becoming the biggest selling film of all time.
Films should be 2D unless it is conceived to be 3D from the get go. Or, if you have someone who knows how to use 3D.