Master of Magic - it’s from 1995, and I probably play it more than all my other games put together.
Asheron’s Call - I let my account go some months ago (and am really regretting it considering recent events in the game) but when I had it I played it a lot.
I really can’t go any further than that, there are no other PC games I’ve had recently that I have played as much as these. I can do honorable mentions, though…
Master of Orion 2 - made by the same company that did Master of Magic, and it has quite a few things in common. My problem with it is in the endgame, the game gets terribly slow when you have 50 or more colonies to manage and space battles involve hundreds of ships, meaning they can take hours to resolve. The game is quite fun if I can manage to win before it gets that far, and those problems are lessened if I play it with a small universe. Damn good game, regardless.
Deus Ex - I loved this game until the last level, where it suddenly got several times harder than any part up until then and I got frustrated and gave up. Haven’t played it since, but up until then it gave me a lot of enjoyment.
Crimson Skies - Everything about this game was nearly perfect. The setting and atmosphere was interesting and fun - it’s set in an alternate universe where the U.S.A. fractured into about 20 independent nations in the 1930s and you are an air pirate. The graphics are beautiful, the gameplay varied and challenging (though not frustratingly so), you can design your own customized airplanes, the controls are simple, it’s definitely not realistic enough to be a flight sim but there are enough realistic touches that you have the feeling of flight. Yet I haven’t touched it since I beat it, except to show off it’s graphics to friends.
Baldur’s Gate 2 - far superior to the first one, that bored me to death. An interesting story, fun characters, huge world with tons of quests yet it never got confusing. I helped my wife play through this one, now that she is finished I don’t really have any desire to complete the game with my own party.
Wizards and Warriors - when I first bought this game, I was very disappointed, did NOT like it, tried to play it a few hours and then put it away. Months later, I decided to give it a try again, and this time it clicked. This is a damn good old school RPG ala Wizardry (in fact, it’s made by the same guy). I haven’t played it lately though, since I am stuck in a part of a dungeon surrounded by monsters I just can’t seem to kill. Sometime when I am bored I will try again, though.