8. Call of Duty: Modern Warfare 2
This instant classic introduced first-person shooter aficionados to one of the most intense campaigns ever.
A darker plot than most, anyone with a conscious will struggle with tough choices very early in the game. The fact that Modern Warfare 2 forces the player to become a terrorist is as uncomfortable as it is genius. If you haven't played Modern Warfare 2, or it's been awhile, pick it up again and see how much it has contributed to the current state of gaming.
While the campaign is short, about 5-6 hours, it's emotionally exhausting, think of how you felt after watching The Hurt Locker, yeah tough.