[ml1201]

Well, Diablo II is free to play and has quests that make up the plot for it. The expansion does also add new content and you can probably get the normal and expansion version cheap somewhere. This game does not require you to play with other people, nor to go online to the 'official' multiplayer things (its called Battlenet) if you don't want to. But you can join friends and stuff through a net connection and have your own game going. XD