Variety and potentially the complexity of games (especially those that include editors), modding communities, occasional unofficial community support/fixes after a developer pulls the plug on a game, hardware superiority (potentially) over consoles, allowing (potentially) better, bigger game worlds, more diverse games, better engines, generally good prices (with the advent of the digital distribution/availability since the past few years, it's now very easy to just wait two or three months until a game's initial price is cut sometimes by as much as half).
What else, oh yes, the controls, a bigger on-line games library, capacity of (occasionally) changing various in-game/in-files settings and variables to accommodate the system's capacities, ability to listen to your own music from background software while playing, save anywhere anytime (in most games, mostly excluding recent console ports, and this is about PC-specific gaming after all)... I could go on and on, I'm sure I'm forgetting something, but there's basically a crap load of reasons why I like gaming on PC and why I keep doing it and stay away from console gaming.