20. TimeSplitters 2 (2002)
If Back to the Future and Quantum Leap had an illegitimate game baby, TimeSplitters 2 would be that time traveling, diaper-filling shooter offspring. The game featured the requisite FPS fare like handguns, rifles, submachine guns, and grenade launchers. Which is un-remarkable, in and of itself, but combined with time travel makes the game an oft-missed classic to this day. If you jumped to the '50s, for instance, your SMG turned into a Tommy Gun. Shooter aficionados still get misty when talking about this title.