Section 8: Prejudice
has only been available via Xbox LIVE Arcade since April 20th, and on PC since May 4th this year, but you'd hardly believe the popularity of this title.
GameSpy have put out an infographic detailing everything from number of kills, to the amount of time you'd need to play to experience every possible combination the game has to offer. It's the final statistic in the image below, and I won't ruin it, but if you guess now you won't even come close to the true gameplay time required.
If you'd like to blow up this image, visit this link
to make it a little easier on your eyes.