Fallout 3 and Oblivion have both sucked in multiple 10 hour blocks of my life. There were some epic 14 hour Halo 2 sprees way back when. Sins of a Solar Empire, playing on a huge map against multiple unfair AI opponents, with everything turned to the fastest speed, usually takes me about 3 ten hour marathons until I control everything. There was also an 8 hour L4D session last weekend.