1. Ultima 4 and 7 (tie) Great sense of exploration, discovery, and accomplishment. I loved the almost mathematical structure of the Principles and Virtues in U4; the whole game snapped together like an elegant jigsaw puzzle.
2. Baldur's Gate 2 Interesting environments and lots of details to explore. Lots of variety in character builds. Lots of interesting party compositions and NPC interaction. Many ways to solve problems. The party becomes very powerful, we get the nice creamy goodies and get to use them against powerful monsters.
3. Wizard's Crown Very good tactical combat system that's intricate without being tedious.
4. Divine Divinity Detailed environements with lots to do and explore. Cute and funny NPCs. It focuses on what's fun about RPGs and strips everything else away. Good UI (except for direct game world interaction, which is fiddly). Lots of different character builds to tinker with. Addicting gameplay that's full of charm.
5. IWD 1 and 2 Decent story and interesting sub quests. The dungeons are well designed and have themes. The fights are more involved and challenging than is usual because they didn't just throw tough monsters at you. They made the fights happen in challenging situations and combined monsters well. Sometimes a simple goblin fight is tougher than you thought it would be.
6. Eternal Dagger Big story. Lots of exploration. Good combat system.
7. Ultima 3 The first game to give a different slant to the "Defeat the Evil Guy" cliche.
8. Baldur's Gate 1 Heya
9. Pool of Radiance (the original, non-crap game) 10. Planescape
... so I stripped down to nothing but a Super Big Gulp cup and rubberband, and ran up the street screaming "Swing me, gringo!"
