You have to have a system.

Once again I have been forced to question what statements are true and what statements are false. Momento was an extreme brain twister at first. The story is told in reverse chronological order. I found this to be an extremely effective way at mimicking Leonards's own "condition". Leonard can only retain information for roughly five minutes. This is why each scene is roughly five minutes long.
Because of Leonard's "condition" he is forced to write everything down on photos in order to remember. This causes many problems for our protagonist. He is easily manipulated by people such as Teddy and Natalie. This manipulation can go so far as to involve the murder of innocent, or not so innocent (we don't know) people. The only thing that is important to Leonard is to get revenge for his wife. His wife was murdered by a John G. but he doesn't know which one. This poses a problem for Leonard. If he does finally get revenge on John G, he never remembers that he has. Therefor his lust for revenge is never subdued.
One aspect I felt was ironic was the fact that he kept mentioning how you had to come up with a system and that's how you could make it work with this disease. Yet he had a system that was based entirely on pens and photos. Without one of those he could not remember anything since his accident. The entire time he would keep saying "you see, you have to have a system" yet the entire movie he is being manipulated to do other's biddings. Some system.
Yeah I guess last but not least, the funniest part of the movie I though was where he was getting chased and goes, "Whats going on, I'm chasing somebody." Get's shot at and goes, "No they are chasing me." Classic.