Morrowind (with expansions) will always have a special place in my heart, but I wouldn't enjoy it if I picked it up again since I've drained that game. The obsession is long gone, but boy was I obsessed with it. It wasn't healthy at all.
Disciples 2: Dark Prophesy comes in second, probably. Highly recommended if you like turn-based strategy.
I enjoy many modern games, some quite a lot, but none have displaced those 2 oldies. Maybe they can't be displaced because of nostalgia.