Oh yeah, game addictions come and go, but for me there has only been one real game obsession, Neverwinter Nights. (nice to see another person on this forum who's been into it
)
I've been so obsessed with it that I learned all the stats (magical properties) on pretty much all weapons, armors and other magical items on the specific server I played on. All those were custom made and are quite a few. I was also very much into the whole game engine and game ruleset. Found it very interesting to discuss character building (which has pretty much endless possibilities in that game.) So yeah, one game obsession over 8 years on mainly one server which is now quite dead. (still up and running but no players)
Other games I've played over and over again has been GTA 1, 3, Vice city, San Andreas and ofcourse the cursed counterstrike 1.1-1.6 >.< Still play alot of CS cause I have alot of friends on the server I play on, so It's kinda my only social activity with other humans that I do.
When it comes to the GTA series I find San Andreas the ultimately best one, as the whole car modification thing (messing around with handling and car models) is so nice to play around with. For anyone who wants to give it a try then check out the Project Cerbera for a complete guide to how it works.
In my earlier days I spent waaay too much time playing games such as Zelda, A link to the past (on SNES), Age of Empires 2 and ofcourse the Warcraft 2 & 3. AoE2 was probably a minor obsession as well, as I memorized the manual (a minor pocketbook more or less) and knew the game inside out.