Oblivion
The fourth game in the Elder Scrolls series, and arguably the best game in the history of mankind. By purchasing this game, you have sold your soul to Bethesda Softworks--which is a pretty even trade-off, actually. Once you start this game--assuming your computer/Xbox 360 doesn't burst into flames of righteous fury due to it's lack of uberness-- you will not be seeing the sun for a while.

Side effects include: Weight loss, paleness of skin, weight gain, reluctance to leave your chair, death, peeing in a bottle, ordering pizza every night because you can't stop playing long enough to make some food, loss of the ability to distinguish between fantasy and reality