This movie was a pleasant surprise. The basic premise of the movie, while having been done before, was executed in a truly unique way (without giving away any spoilers). I also didn't feel like the movie had any holes; it was, all in all, a very solid movie. Furthermore, I felt that the plot was extremely intellectually stimulating. The movie constantly kept you thinking -- if you are inclined to do so -- about what was really going on, or what might happen next.