What Nolan does in this film with time is incredibly innovative and original. The film's main plot unfolds in 10 to 15 minute fragments given in reverse chronological order (Leonard's hunt for John G.). These fragments are shown in color, and punctuated by a chronological subplot shown in black and white ( the ongoing telephone conversation in which the story of Sammy Jankis is revealed).This subplot gives back-story and context, but also provides cohesion to the main plot fragments, which is particularly helpful in the earlier parts of the film. Further comprehensive aid is given through the editing technique. Each successive fragment happens earlier in time than the previous one, but, the final moments of each fragment overlap or repeat the first moments of the previous fragment, connecting them and providing a sense of bearing . While the main plot and subplot unfold in opposite directions in time, a second subplot emerges. It is a reoccurring scene that starts with a closeup of bathroom tile, showing a little more of the scene each time until the entire scene, of what appears to be the murder of Leonard's wife, plays out. So, the involvement required to keep the plots sorted connects the audience in a way that just isn't typical of most films. This connected vibe is amplified by the fact that the audience is experiencing the film in the same way that Leonard experiences life--in confused 15 minute fragments. Thankfully, we are able to string those fragments together without Polaroids or tattoos.
So, is that it? Is Nolan's innovative time manipulation device or devices what make this film remarkable? Of course it is a great story with fascinating characters, and superb acting. But I think there are also intrinsic elements in the story that connect with everyone, contributing to the punch this film packs. In order to avoid a lengthy digression, I will simply pose two questions that the story provokes: 1) To what extent does our conscious memory constitute our identity? 2) Do we lie to ourselves to be happy? When considering this second question, I think of happiness in the Epicurean sense--equivalent to the absence of pain.
Leonard is the extreme example, willing to go to any length to maintain the absence of pain.
So, I think it is Nolan's manipulation of time, but also the story, the great acting, and the universal themes to which everyone can relate joined masterfully in concert that make *Memento* a brilliant memorable film.

