This film stretches its premise so far beyond the realm of reality and my suspension of disbelief that I don't even know where to begin. No matter what angle I try to attack this story from it doesn't make any logical sense. Plus the pacing is horrible, and all the repetition (while it makes sense story wise) becomes tedious very quickly. Like American History X it's black and white section is gimmicky and pointless.
I've always wanted to love Memento because of its ambition, but its execution always bugs me. It's too slow and it babies its audience in the tails of each scene change. Though it's disappointing that Pearce's Lenny is the only real fleshed out character, Pearce is effectively able to carry the story. Its interests in memory beyond its formal conceit/plot gimmick is fascinating, but the gimmick is what you remember.
A movie that takes the audience on the same ride the character is on which is rare when taken to such an extreme as this. On the first watch, it takes a bit to get emotionally invested in the characters considering the odd structure. Each scene you're trying to piece the scenes in chronological order and put the pieces together which doesn't leave much time in the beginning to empathize.