Original: Half-Life

Half-Life set the bar for shooters for years afterward. Te never would have predicted that Valve could make a game that groundbreaking twice, but Half-Life 2 was a massive transformation for the series, and if anything it proved even more influential than the original.

Half-Life protagonist Gordon Freeman still wouldn't speak, but every other character—even some unnamed scientists from the first game—was given new life in Half-Life 2. The environments were more expansive and far more detailed, the story was bigger and better, and the graphics were insanely good at the time.

The Half-Life sequel is also praised for its strong female character, Alyx Vance, as well as its innovative and unique gravity gun. Now if only Valve would finish the story!