Well, Oblivion got me into gaming, and as they say, the first time is the one you remember (or something like that). I strung OB out for over a year with mods, then played Morrowind. Quite a story line, and I enjoyed it, but it was dated compared to OB. Still on the favs list though.
The Witcher had my top vote (after the bugs were worked out in the Enhanced Edition), and now it's Dragon Age: Origins, and Awakening, and all the add-ons. I can't wait for DAO2 in February!
Of those, I remember The Witcher most, and I just visited the forum recently (checking release for TW2) and downloaded a couple of mods that have been created in my absence. Time to reinstall the game and try them out!
Finally (and I know it's off topic for this post), if you've never played Half-Life 2 (and you think you don't like FPS games) get this one (the price is right these days) and play it now! I'm really enjoying the ride, and the game looks and plays beautifully.