If anything, Natali is the most economically prudent of all directors. As in Cube he used the claustrophobia of a box (this time an elevator, hence the uninspired name of the movie) very well. It makes you cringe when a guy says "let's not panic" in a panicky voice in closed quarters. Being locked in with a monster is scary, but being locked out of where the monster is can be just as scary. Can be used in classes to show how to make a short movie.