TF2

Team Fortress 2 with 750 hours. :)

Counter Strike 1.6 (590 hours) :D

Call of Duty MW2 multiplayer (1414 hours) :)

Counter Strike 1.6 -> 3,746 hours
Counter Strike GO -> 1,185 hours

The Binding of Isaac: Rebirth
thanks for giveaway

TF2 & CSS

GMOD 705 hrs

Team Fortress 2 = 4415 hours
Left 4 Dead 2 = 4065 hours

Fallout 3 - over 500 hours with DLC and mods

WC3 or NS2.

Witcher and Batman series

Still TF2 - over 326 hours

I believe Path of Exile, 932 hours on Steam, and at least as much on the standalone client.
Thank you for the giveaway!

Thanks for the GA
Command and Conquer Renegade, 9000+ hours, I was a server admin and in game moderator for 6+ years.

Dota 2 - 988 Hours
Cs;Go - 500 Hours
World of Warcraft - 15000 hours

Company of Heroes 2

Borderlands 2

Gothic 2

DayZ and Fallout

On Steam it's currently Terraria (150 hours and I still suck! xD)
For a long time, before I got Terraria, I thought that my most played game all time was Skyrim (which now has 141 hours) but then I wanted to play Dissidia Duodecim on PSP and I have 300 hours on that.
I can't imagine I played that for 300+ hours and I didn't learn to play it, lol. But ya know, same goes for Terraria.

Skyrim

Guild Wars

Skyrim, Fallout 3, Fallout 4, Lineage 2

Left 4 Dead 2 <3