Memento is incredibly powerful because of its sequences of flashbacks. The movie has scenes in color that slowly go back farther into the sequence of events that led up to Leonard's killing of Jimmy, but at the same time has scenes in black and white that depict Leonard telling a parallel character analysis of Sammy Jenkins over the phone to an unknown listener. The scenes ultimately intertwine together to create a "present" time encasement. The black and white flashbacks master the art of lighting and shadows and set the tone for a dreary plot. Nolan creatively develops a new method of filming and storytelling in this masterpiece.
Perhaps the most confusing twist in the entire movie, though, is when Leonard nearly consciously decides to choose Teddy as his next victim in his series of murders to avenge the "murder" of his wife. It is the only point in the movie that the audience shifts from pitying Leonard and accepting his amnesiac handicap to wondering if Leonard controls his own twisted fate. It is ironic because every character in the movie takes advantage of Leonard's memory loss to carry out their lowlife needs, but Leonard himself takes advantage of his own condition because he leaves clues for himself that point to avenging his wife's death over and over again. In effect, Leonard uses himself, too. He is never content with killing his wife's murderer, for he is not able to remember the emotion of having even completed this task. It is a twisted movie that is left open for interpretation to this day. Its unique film style transcended the films of its time and went on to inspire films like The Sixth Sense or Vantage Point.