Well Nikitson,, I think with that question u set a new hot thread in here. Hmmm..., I can´t say that there really is a favorite game. I like many games, like Final Fantasy 1-12, I´m still waiting for Final Fantasy 13 (+ all aditionals like Agito and VS). Hmm..., hard :xx:. I like the Zelda-games, and also Mario, Parasite Eve 1+2 (PSX), Resident Evil 0-4(yes there was a "0", it was on GC and give a co-op factor to the game, but not rly), and still waiting for Resident Evil 5. Well, there are also may oldschool games I like. Like Terranigma, Secret of Evermore, Secret of Mana (and Seiken Densetsu 2nd part of it), then I like Beat´em Ups like Tekken 3-5 , Soul Blade (was the first "Soul" game which appeared on PSX), Soul Calibur 1-3 (havent played 4 yet :(), F.e.a.r + all addons, but only on extrem Difficulty without slomotion (makes the game more realistic), and DOOM 1-3 (mostly 3 coz of its modfriendly engine) . OMFG..., there are to much. 
Hmm..., Quake 1-4, specially the Arena-games, UT2k4 and 3, Diablo 2, Legend of Legaia (also a PSX-game), ---I also like CS and CSS--- (but I havent bought it in seam yet -.-), Dead Space, Prince of Persia (such a great game).
Okay guys this are just a few games on my list. I rly know much games, coz I played alot (also trash), but one is for sure. All games which appears in here, are worth it to play them once. Maybe there are some which I forgot but fact is, there are many games with great story, system, grafix, and so on... 
Greetz ur leader
Max Payne, Team Fortress 2, Guitar Hero III, Zombie Panic! Source(this game so funny and everybody can download this game in steam like Age of chilvary) im waiting for Alan Wake.. i think it will be nice game.
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So anyone who feels like up for a good game, come and play with us =D 