The performances are compelling, the plot grabs you by the neck and won't let go, but the star here is the story. The movie begins at its end. That's right, the first thing we see is the climax. Lenny murders Teddy. I told you, that's the first thing you see.
Memento works in reverse.
It flows backward, showing us a sequence of events not as they happen, but as they have already occurred. First, we see the murder, then we learn what led up to it. Then, we go further backward in time, to learn the significance of the murder. This sounds like a first time director, playing with the medium, but it's not. Christopher Nolan has chosen exactly the right way to tell this particular story.