I am not saying that no movies should have sequels, just that not EVERY good movie needs one. Sequels can be good movies, but some originals just tell the right story, and adding to it would simply detract from what the first movie accomplished.

12 Monkeys is another one. I know they made a series based on it that a lot of people liked, but I think it was long enough after the original, and changed enough stuff, that it wasn't really a direct sequel.