2. 'Gears of War'
"Reloading guns" is an unlikely space to find room for innovation, but Gears of War managed it with the active reload system, which rewarded players for a well-timed second press of the reload button. It's surprising more games haven't copied it. Active reload gives players something to do while hunkered down behind cover, which is what Gears of War is mostly about. While blind-firing over walls had already been done in Kill Switch and The Getaway, it was Gears of War that popularized this style of third-person cover combat and made it the standard mode of action games for years.