Most Addictive Games

[UltraWar]

Hearts of Iron II: Doomsday - SO addictive!! Must not play as Soviets anymore, eyes burning! No must take England! :grrrrrrr:

One day, I'll actually be able to start to mod the game.

[TevashSzat]

There are only two for me:

1) Diablo II LOD (I have tried to quit for so long, but I always end up playing again)
2) Starcraft Brood War (Very fun normal games as well as awesome custom maps)

[TinCow]

I guess the addictive nature is best judged on how many times I replayed the game. By that standard there are a few top contendors:

1) Civilization Series (Civ 1, 2, Alpha Centauri, 3, and 4) - I have put in massive amounts of hours on every single one of them. Easily the top time consuming game series for me.
2) Baldur's Gate Series. I've probably played both BG1 and BG2 half a dozen times each. Possibly more for BG2. I doubt I'm done with them either.
3) Q3F - The most time I've ever spent in any online game. This later transferred over to Desert Combat and BF2, but Q3F dominated my life for a good 3 years.
4) Ultima Online - Two years of my life vanished in this one. Also the main reason I stay away from MMOs now: I've experienced the time commitment required for them and don't have the ability (or desire) to do so again.

[Quirinus]

I'd say:

--Galactic Civilizations
--Rome: Total War

These two games I have played again and again and again. To a lesser extent, I also used to play with Jedi Outcast: Jedi Academy, Empire Earth and Warcraft III a lot.

[Evil_Maniac From Mars]

World in Conflict
Hearts of Iron II (been playing since release date, haven't stopped once)

[Ser Clegane]

One of the most addictive games for me was HOMM 3 - never experienced the "one-more-turn"-syndrome to such an extent.

Other games that I spent a lot of time with (and keep doing so every time I revisit them):
- BG2
- Civilization IV
- Fantasy General
- Tie Fighter
- M:TW