Unreal Tournament 2004 4000+ hours when it was being counted by Xfire. The best gaming years of my life were with UT2k4.
I got like probably 500 between and the trails games. That being 8 games deep and waiting for the trails of steel game that hopefully comes out this year.Going way back, untold hours on the earlier Pokemon games.
Steam says 131 hours on Skyrim. That's not counting consoles.
166 hours of Fire Pro Wrestling World.
Nearly 70 hours of Civ V
Over 120 hours for Trails in the Sky (all 3 chapters).
I'm sure games like Chrono Trigger, Sonic Adventure 2, or Knights of the Old Republic would exceed 50 hours if one tallied up multiple versions.