Se7en is no less than a master piece by David Fincher. The gripping ambiance, the sheer genius of the scenario as well as the acting power of Morgan Freeman, Brad Pitt and Kevin Spacey are it's strongest point, but there's no aspect that is less than great. (Except for one very minute detail.) One thing that is often overlooked is the backdrop discussion on society by the main characters which makes the movie that much better.
A must see if you don't mind harsh crimes.