23. Team Fortress 2 (2007)
We love it when an FPS adds an element of strategy to the action, and no game does it better than Valve's PC standalone Orange Box component Team Fortress 2. Your team of Saturday morning cartoon reject mercenaries must utilize their specialized class powers effectively to push back invading enemies. Plenty of twitchy gunplay combined with individually focused talents made TF2 a contemporary influences on dozens of clones. The overall aesthetic and tongue-in-cheek humor combine to make Valve's shooter a cherished game to this very day.