1. Call of Duty 4: Modern Warfare (2007; PC, PS3, Xbox 360, Wii, Mac)
This is the game that turned everything around for first-person shooters and much of gaming in general. Up to this point, Call of Duty had been a World War II military shooter with admirable attention to detail. But Modern Warfare set single-player and multiplayer expectations to new levels. The modern setting did a lot to ratchet up the intensity, offering political intrigue between contemporary powers wielding imposing modern military weaponry.
The role of multiplayer mode in doing so was just as important, as it popularized features that would become standards in shooters to this day. With killstreaks, weapon attachments, weapon loadouts, player experience levels and the prestige system, among other standouts, Modern Warfare laid the foundation that other games would build upon for over a decade.