as many have mentioned, the D&D games.

Baldurs gate 1 has an awful storyline really, however, it is imo, one of the most enjoyable games ever made .. when you reach the end of bg 1, a storyline begins to take form and then you will venture into the interesting world of the bhaal spawns.
Icewind dale , plansescape torrent are both very good games as well

Morrowind is a must and a wonderful game

What I didn't spot at my quick glance over the thread, was the final fantasy series and Chrono trigger?? Chrono trigger has perhaps the best plot and storyline I have ever seen in any game.. and Final fantasy is always fun, unless you forget to pick up the super duper weapons and get smashed by the overpowered enemies