49. Unreal Tournament (PC)
This game was a revolution; the first game marketed as a pure online shooter. Fast paced action, multiple game modes, superb level design and a plethora of weaponry made this game sublime. Unreal Engine and Epic would never have been so big if it hadn't been for this game's success.
Clue for 48:
This 2D game was re-released on iOS and Android earlier this year.