Quake

Worthless singleplayer with a story that seems to been done on a coffee break. In singleplayer you explore four different episodes with a number of levels and the goal of each level I simply to shoot your way to the exit. At the end of each episode you find a magic rune that you take with you and when you have all four runes a secret path in the hub that connects all the episodes open up and you can go and kill Shub-Niggurath, the final boss. The singleplayer campaign can also be played in co-op and it makes it a bit more fun :).

Multiplayer is deathmatch and fun but the thing that made Quake epic was how easy it was to modify and the number of modifications that was made for the core game.