chautemoc: All good titles, but I'd vote Arx and UT2K4, for sure -- Arx is a great and innovative first person RPG and spiritual entry in the Ultima series..UT is arguably the best online shooter Epic's ever done (as is my understanding). :)
Gorky maybe -- try the demo to decide. As mentioned, there is a rather pesky problem with it. Can't comment on Kingpin but it does seem like a pretty good game, albeit with major flaws.
Yeah, I just read the Arx Fatalis review on gamespot, and it sounds amazing. demo first as always. =) AS for UT2004, I need to play with my mouse BEFORE I buy, because it runs perfectly yet aiming is a bitch with a mousepad.