For single player, it's a tie between Banjo-Tooie and FFXII. Both of those games just click with me way more than any other game I've ever played, and they both blow almost every other game out of the water for me in terms of hours played. For multiplayer, it's Starcraft 2. I doubt if there are 3 other games that have even half the hours logged that I have for SC2 (and 2 of them would be Banjo-Tooie/FFXII).
For single player, it's a tie between Banjo-Tooie and FFXII. Both of those games just click with me way more than any other game I've ever played, and they both blow almost every other game out of the water for me in terms of hours played. For multiplayer, it's Starcraft 2. I doubt if there are 3 other games that have even half the hours logged that I have for SC2 (and 2 of them would be Banjo-Tooie/FFXII).
Pretty hard to pick, since I probably have a couple favourites in each genre that are kind of hard to compare, being completely different types of games.
But if I had to pick I would say the Civilization series - specifically I spent the most time playing Civ2 - However, I've spent countless hours playing Civ 1,2 & 3. And more recently I bought Civ5 and liking that too.
Honourable mentions:
Fallout (ALL)
Elder Scrolls (ALL - but particularly Morrowind - especially with all the excellent MW mods that were available in the day).
Deus Ex (ALL)
System Shock 2
GTA (ALL)
I never got into the MP scene, so my picks are all about a good SP experience.