If the game is a fast paced, action game I usually play it for 2 - 4 hours per sittings till the game is finished.
If it's a game like GTA, SSB, mario party, etc it entirely depends....if i'm playing alone I may not be able to play for more than 15 minutes but if their is a couple friends playign with me we can play for 3 - 5 hours before getting bored with it.
If it is a sims game or anything like it I can play for up to at least five hours, I entirely lose all sense of time when I play those games and they take a while to get boring because their is always improvement that can be done to your character, realtionships, cities, chouse, etc.
In a game that is the opposite of the first type I listed I like to play them in hour sittings for several weeks.