Grim Dawn: 2544 hr
Dota2: 952 hr
Civilization 5: 805 hr
Skyrim: 592 hr
Torchlight 2: 470 hr
It’s difficult with pre-steam stuff. Like, 952 hrs in Dota2 is a joke compared to how much I played DotA1, and with other custom maps and the time I spent in the editor trying to learn mapmaking I think Warcraft 3 easily beats my Grim Dawn time. Grim Dawn had been my favourite game for 2.5 years, with some breaks, while WC3 had been my favourite game for like 5 years. So… 5k hours perhaps?
I was also fiddling with Heroes of Newerth for like 3 years, which I had also played almost dayly, so it should be close to GD, if not bigger.
Also, I was playing both the disk version of TQ and steam, so total time should easily surpass my Dota2 time too.
As for the pre-PC era I can’t even fathom how much I played Final Fantasy 9, Digimon World 2 and some other JRPG.