Let me see... longest game time ever I think was Mod Nation Racer at over 300 hours.... I know, but that game just kept sucking me in. Starhawk is my close second with I wanna say around 250 hours +/- but I can't say for sure. Oh and GTA4 I lost count with that I'm sure it is actually prolly number one, but I lost track after awhile.... now that I think I'll wager it's over 300 as well.
Probably Dragon Quest VIII with about 130 hours. Had no idea that game went into such depth with the Dragovian Trials at the end. Second place is probably Star Ocean: Till the End of Time and Final Fantasy XII, each with over 100 hours.
But then I see the amount of time some of my friends put into COD and it just blows those hour counts away.
I remember looking at my amount of games played on the leaderboards, multiplying that by the average of time played per game and thinking, "Holy crap that's alot of time played." Far more then any game I've played up until then, and even up until now. I couldn't believe I had played well over a months worth of hours in one game. Probably close to 1,000 hours. I was almost embarassed with myself... almost.
Needless to say, I made sure my Wife never found out. lol.
I did 270 hours in "Final Fantasy Tactics". There is a side quest in that game where you can make a Final Fantasy 7 character a playable character in Final Fantasy Tactics. And when a got the Final Fantasy 7 character they were at level 1, so I had to level them up so they could fight in the final battle against the final boss. It took me an entire summer to finish that game.