Got it for my birthday (August). Had 4 nights in a row in which I stayed up until 4am.
Purely out of self-preservation, I have not returned to it since.
I mean, sure, WarCraft III kept me up late several nights running, too, but at least it has an ending. The Sims pushes more buttons than I knew I had, and it goes on forever.
People! People! Let’s not forget Tetris! I know it’s been a while, but hoo-boy!
I’ll second Subspace/Continuum. Great game that you can jump in, kill some ‘noobs’, and jump out, all during lunch break. I can’t dedicate my life to Red Alert, Total Annihilation, and Counterstrike like i used to.
it’s free and fun.
Well Swashbucklers was the first addiction, many moons ago.
Then Rescue Raiders.
The Pirates.(It was so much fun having a War Galleon, with 300 fully armed Soldiers surrender to my Pinnace with a boarding party of 12, just cause my rep was so badass, and I took their captian down in 3 seconds.)
Them Sim City and Civ
then Civ2
the Everquest.
Civ 2 was my favourite but that’s been bumped by Europa Universalis II.
Its just too easy to fall into trying to make Sweden the owner of all Northern Europe or raise the standard of the Papal States, over and over and over and over again. 
Another vote for Masters of Orion. I refused to “win” the game by being voted ruler. I had to take over every planet. This meant constantly voting against myself.
Of course, when I voted against myself the others would get furious and attack me. That’s a pretty funny reaction, isn’t it?
I also had a lot of trouble with The Sims. I finally learned to set a timer when I was playing. When the timer went off, I had to stop for a bathroom break.
All the Civilization games. I had a twenty page paper due, and I kept telling myself “I can quit whenever I want, just as soon as I conquer the Persian infidels.” Gah!
Tetris, definately.
Don’t forget the various Windows card games.
SimCity I, 2000 and 3000 - not sold on 4 yet
Civilization I, II, and III
Colonization
X-Com
RailRoad Tycoon
Master of Orion
Pirates!
Empire
Sword of the Samurai
Halo, though it’s not a PC game
Jedi Knight
Total Annihilation
Wing Commanders I, II, III
EverQuest
Rollercoaster Tycoon
TIE Fighter
Red Baron
Secret Weapons of the Luftwaffe
And of course, on the TI-99/4A, Tunnels of Doom.
My God, the lost hours of sleep.
Umm…
Space Invaders
Asteroids
Combat
Adventure, even
Up until recently it was Neverwinter Nights. Staying up until 4 or 5 AM when I have class the next day…keeping in mind that I also usually didn’t do the homework for the class. And going at the current trend I’m on now, Sim City 4 and/or Age of Mythology will get me next.
Starcraft. Man, I must’ve wasted 4 years on that stinkin’ game.
Diablo II (and LOD)- I of course, couldn’t bear to play with strategies which were in any way popular or easy. I hung up my Silks of the Victor for the very last time with three lvl 80 or higher Paladins and a lvl 81 Spearazon.
I love Blizzard games, and thank god I wasn’t as hooked on Warcraft 3 as I was on other Bliz games. I broke the chain!
[small hijack]
Wow, there’s a rare machine.
[/small hijack]
Colonization and Civ 2
The strange about both of these games is that you could really at any time walk away from the PC and not have to press pause. Any time you get up and say, go to the bathroom. But NOOooooooOOOOOOoooo I would sit there bouncing one leg up and down with my eyes glued to the screen unable to leave.
Then there is the original X-Wing.
Well, Quake 3 is still sucking years off my life.
I knew that it was time to quit when I was walking down the street and kept trying to fit game pieces into shapes that I saw.
"Ooh…a long one will fit between those two cars…and a square between those two houses!!
Basically any good console RPG game (FF, Chrono Trigger, Breath of Fire, etc…)
However, the award goes to the crackiest game of all, Evercrack (Everquest). I don’t play many computer games, but I played this one for a good year and a half and played it EVERY day, routinely 15 hours a day and sometimes whole days at a time…I’ve been off it for about a year and half now. It’s a very evil game and I will not touch it. Be very afraid.
Teebone
The naval simulation Harpoon .
I still keep a 386 going just to play it.
Sad, really…
Space Empires 4. if i play that, i’ll still be playing at 7am, wanting so bad to be able to stop and go to bed but unable to draw myself away from the screen.
Caesar III
Pharaoh
Jedi Outcast
and my newest timewaster…Yahoo games has one called Dynomite. I have played it so long that I dream about little brightly colored dinosaur eggs.
Civ and Civ2, the former slightly more than the latter as a big game in Civ2 does take bloody ages to finish, though the game’s a goodie for all that.
Elite and Lords of Midnight, from the good old cassette days. Yes, I managed to crank out a win at LoM within a fortnight of opening the box, but it had amazing replay value just trying to do different things, such as weakening the Ice Fear enough that the craven Lord Trorn could be persuaded to attack Ushgarak.
Might & Magic 6 and 7, both. Also Heroes III and Armageddon’s Blade.
MoM a thousand times over. It’s amazing how many different killer stratagems you could come up with. I liked Runemaster/Artificer for the ridiculously cheap items you could make; White warlords with Crusade, Holy Arms and a few Altars of Battle to pump up the favourite units (Halfling Slingers were surprisingly good; that +1 To Hit and Lucky covered a multitude of sins; and I once enjoyed some success with Champion-level Rangers, which were normally quite dismal); and, of course, the heroes. Torin was extremely good (no duh) but I also liked Warrax for his armour-piercing zap - it could punch through Magic Immunity once he had some worthwhile items - Malleus for sheer firepower, and on one never-to-be-forgotten occasion Mortu the Black Knight acquired enough speed and punch that he could take out a stack of Sky Drakes single-handed. He was fast enough to run up to them, take a Drake out with First Strike and then flee out of range in his remaining half-move. What joy.
And of course beginning with 11 black books and whistling up a single Wraiths unit that not only took out neutral and enemy cities alike at that early stage of the game, but left undead garrisons behind…
Ah, happy days. But it was no treat to run. I had to make up a special boot disc (I have it still, for old times’ sake)…
Stop! Stop! Shut up about MoM!!!