misteryo: The unspoken first part of this question has to do with genre.
I love big rpgs more than any other type of game. Sure, Doom II is damn near perfect, and sure I spent hundreds of hours in Civ IV, but as good as those games are, I don't love them as much as I love rpgs. I love creating characters, poring over stats to better understand the game mechanics so as to inform my choices. I love the thrill of entering a big save-the-world quest. I love the interplay of combat and dialogue and crafting and inventory management.
So, among big rpgs, for years I have said Arcanum, and I'm going to stick with that choice. I no longer play it. Maybe I will some day, but I spent so many hours playing it that I believe I have exhausted the HUGE amount of options for character creation. I have exhausted the different questlines and mutually exclusive choice-paths. I have played through as an idiot. I have finished the game as both a technologist and as a magician. I love the setting. I love the soundtrack. I love the Virgil storyline. I love the electric tophat. I love the jokes. I love the dialogue. I love that game.
Pretty much the same for me. I love RPGs for all the same reasons and spend a lot of time just reading the manual (remember those) before I even hit New Game. However my RPG's of choice are Fallout 1&2. I got both when they were new releases and have replayed the a few dozen times each, going through all character archetypes I can imagine and even did a few runs with the most inefficient character imaginable. Basically I looked at what online boards were calling the worst, most useless skills and traits the built my character around them.