Morrowind really is as addictive as Xena describes. The game play is unscripted. There are tons of quests to follow, which gain you experience, cash and open doors but you don't have to follow them, you can just wander and explore if you want and there's lots and lots of exploring to do. The game is frustrating at first because your character moves so slowly but that changes as your character gets stronger. I probably spent a month of actual game time playing Morrowind and never got bored with it.
I'll definitely give Morrowind and Dungeon Siege a try. I have to stop playing Diablo II long enough to actually load the CDs, though...LOL!