10. Cover System
We've all played arcade games like Time Crisis 3, where a gunner has to pop out from hiding to blast away at his foes. Companies like Epic Games utilized this mechanic in their highly anticipated title, Gears of War. Of course, they weren't the first to implement said mechanic into a game, but they really revolutionized the cover system by allowing freedom to move while in cover and to have the ability to perform different actions while behind cover. If you wanted to jump out and shoot Locusts in the face from afar, you could do that. If you wanted to hop over a fence and chainsaw your enemies in half, you could also do that. The cover system created a new experience for FPS enthusiasts and allowed them to play the game with a different aspect to consider.