About twelve hours or so. The only reason I even played that long was because my roommates kept insisting we play that instead of anything else.
I couldn't even finish the single player mission on that game, much less prestige in multiplayer. It wasn't any fun unless you put the effort in to make it ridiculous, and even then it was mediocre. Running around with tomahawks and the crossbow in every game was about the closest I got, and even then it was a very meh experience. The maps were horribly designed, emphasizing CQC over everything else, snipers (typically my weapons of choice) were beyond useless in any situation; completely inaccurate at any distance, wouldn't hit the cross hairs unless you waited about fifteen seconds between shots, and couldn't even kill in one hit unless you got a headshot. Stupid design choice for a game like that.
I could go on for quite a while, but I'll cut it off there. I hit the end of the first level-up cycle, looked at the option to prestige, and laughed in its face.