Another strategic RPG lover over here: Disgaea, Phantom Brave, Vandal Hearts, HoMM, Fantasy Wars... Love them all!

Adventure games! At least the good ones:
Lucasarts classics (Day of the tentacle, Grim Fandango)
Sierra Classics (Gabriel Knight series)
Homemade games (Trilby-series)

Currently, I'm hooked on FPSes. However, I do have a soft spot for 2D side-scrollers.

FPS and RTS games.
I also like RPGs, Racing games and platformers.

Any reason, why on GOG of all places, you forgot Fallout Tactics?! :)

Ah, was wondering reading through this when I'd see those pop up. Wholly agree with you on those, as my gaming obsession is pretty much replaying those over and over again, even though I know how they end. Odd, but they were more or less my introduction to storyline gaming - which is the second obsession.
Give me a good, well thought out storyline, and I don't care what style of game I have to play through to get to it!

My obsession is buying every game made by Valve and trying every mod there is.
Also, achievements.
Whenever I get the chance, I brag about the Vanilla Crazy Cake I earned.
...
See, there I did it again.

I like them heavier RPG games. Baldur's Gate, Fallout, Might & Magic. Games with a deep story, Lore, Epic feeling to them.
Mostly anything made by Black Isle and some NWC/Bioware games tend to get that well. Blizzard too i guess, But thats less RPGish.
It's all in the details.

I loved the Fallout series (mixed feelings about its latest incarnation...), most Bioware RPGs, tactics games in the vein of Battle For Wesnoth and Final Fantasy Tactics, strategy games like StarCraft, Command and Conquer, and Original War, sci-fi "simulators" (Mechwarrior, Freespace), most first-person shooters, retro-ish 2D shooters reminiscent of Tyrian and Raptor...
and Halo.
Everyone has something they're not exactly proud of, haha.

While I do play many of the "big" games, I am also a lot into "indie games", games developed by independent developers, mostly single persons or small teams, and mostly in their free time.
Notable examples are games like Cave Story, the amazing Dwarf Fortress, Knytt Stories, , [url=http://datarealms.com/games.php]Cortex Command and basically an uncountable amount more.
While I am not a developer myself it is still great to be part of communities like [url=www.tigsource.com]The Independent Gaming Source[/url], where it's mostly really all about the "spirit" of gaming and seeing the games as works of art :)
As for game genres in general I am hardly focused on anything specific. But I do greatly enjoy tactical games, especially squad-based ones like X-Com: Enemy Unknown, turn-based strategy games and hybrids of strategy and action, like Sacrifice and Hostile Waters. Thanks to GOG I finally got to playing the latter :)
Those are surely not the kinds of games I play the most, but they do get my special attention :)

Space 1889 and Megatraveller 1 & 2
I think you'd enjoy the char creation there. Those three games I really enjoyed creating my chars. Those are also 3 games I home come to GIG.
As for my obsession... I don't think I really have one. I play too many different types of games to really focus on one game. I like FPS (Crysis, Call of Duty), RTS (although its my less played genre), MMOs (UO and waiting for Darkfall), strategy (Civ series), soccer manager (Soccer, by Wizard Games is my favorite), trading (Merchant Prince II), hell I eve play a lot of Solitaire.
Maybe my obsession is reading, I've been pretty much nonstop reading since I was in elementary school. I used to read 5 books a week, now its down to about 2. Mostly military based, sci-fi, fantasy, historical fiction, nautical fiction, stuff like that.

My gaming obsession? Older games. Rather appropriate given the forum, I guess.
I don't own a 360 or a PS3, and neither of my PCs are spec-heavy enough to run anything major released in the past three or four years. And to be honest, I'm quite happy with that. I love hunting through piles of used games for that gem that everyone else passed over, or finding sites that this that can sell me older games that I either loved at the time (Sacrifice) or had a demo of and always wanted to play (Fallout Tactics).
Luckily my fiancee is also a gamer and shares my obsession (even if she mixes said obsession with JRPGs of all shapes, sizes and vintages). In fact, we recently started a classic gaming webcomic at www.generationminusone.com (apologies for the shameless plug ;) ).
It's a shame that there's such a taboo regarding classic gaming. I guess compared to movies and music, gaming's such a technologically-driven medium that anything not 'current-gen' is looked down upon. But imagine not being able to experience films like It's A Wonderful Life and Casablanca, or even The Godfather, 'just because they're old'. It makes little sense in the long run, and hopefully the classic scene will widen over time.
And sites like GOG, and Nintendo's Virtual Console, will be at the forefront of it all. Speaking of which, I'd better go download Mega Man 9 ;)
Teph

Space combat simulations:
Tie Figher (the original, not the rebuilt one on the XWvTF engine); FreeSpace; Babylon 5: I Found Her, also Descent.
The reason people think I'm crazy? Paid ~$140 for a Saitek X52 Pro specifically for (at the time) 1 out-of-print game: FreeSpace2.
Well okay, it's lovely to have HOTAS controls in BF2142 also :)

im obsessed with ALL games the only ones i dont play are some sports because i was never good at them

Any fan of Total Annihilation here (or SupCom :) ) ? Because that is my all-time gaming obsession, and futuristic RTS in general (Homeworld series, Haegemonia etc.)