does the job (exceedingly well)

Rating: 9/10 (5 November 2002)

Like Kristina says, don't read the other comments here; they'll tell you too much.
The other important thing that I think a lot of people don't realize is that there are no complete solutions to what happened in the movie. If you watch the dvd there's an interview with the director and he points out that his goal was to put the viewer in Leonard's shoes. A very big part of being in Leonard's shoes is being confused, lost, and not having control of what's going on.
At the conclusion of the movie you'll feel confused and lost as well; don't take that personally, just consider how effectively the director did the job of making you feel that way. And how you won't be able to stop thinking about the movie for quite awhile.
Don't try to solve all of the questions you're left with; many are meant to not have solutions.