I choose a movie based on several criteria. My latest passion with cinema is Computer Generated material. I SOOO want to see "Avatar" based on a "behind the scenes" look at how the movie was made. But I will also base my desire to see a film on the actors, the story writer, the producer, the director, and how much technical effects the film may have. If the acting is poor but the CG or mechanical effects are outstanding, I'll still enjoy the movie. If the producer is someone I know has done quality work in the past, then I make an assumption that this film can't be that bad. The same idea goes for the director or the story writer.
As an example, I have yet to see a movie with Jonny Depp in it that I didn't like. Probably my least favorite one was "Cry Baby" but that's was because I don't like 50's pop music. Sean Connery, Stockard Channing, Demi Moore, Sandra Bullock, Tom Cruise ... a dozen or more actors or actresses on this list.
Brian dePalma is a director/producer whose work I consider first rate so if he is producing something, even if the trailer leaves me a little flat, I'll probably rent the movie anyway. The same goes for James Cameron (the main reason I wanted to see "Avatar"). I also like Scott Stewart.
If a personality can't hold the movie for me, then photography and special effects has to. Fall on all 5 catagories and it's a dud of a film.