well, depends on the game, sometimes I can play my RPGs for 8 hours straight, sometimes, even if a game is one of my favorites an hour or less is enough. Some of my favorite games aren't that long to begin with :) plus I also rarely replay the long ones and since I mostly play RPGs, those usually get only one playthrough since I take my time to finish them.
Short games, however I can play quite a few times, I've played and finished Silent Hill 2 around 10 times, ICO
around 5 and I used to play and beat Rez every day at least twice for about 6 months back when the game came out for
PS2.