What do you mean Number 1? lol...You got to be more specific....unless genre doesn't matter to you. When it comes to perfection, there is no such thing as a number 1 PC game. It's more of a opinion....I don't have opinions, I got facts on what games are good even great but....PC games have been around for decades.....a lot of games have been "ported" to PC which doesn't even count as a PC game because the original source is console. If I was to choose top PC games, I look to the past. Back to DOS games. Commander Keen is a GREAT PC franchise game I recommend. Hexen 1, Heretic 1 are both epic first person games.
