I wanted to post in that Top 5 games on Steam list, but for some reason all oldish threads on there are locked now.
So my top five are:
New Vegas - 343 hours, not even considering all the hours played on Xbox and though mods
Warframe - 284 hours, though that's not much compared to those on here
Mount and Blade: Warband - 121 hours, plus some with mods
War Thunder - 112 hours
PUBG - 89 Hours
Most honorable mention goes to S.T.A.L.K.E.R. though, with 39 hours for the base game, with a few additional hours due to the sequels/expansions. I've put hundreds of hours into mods like CoC,Dead Air, LA, etc., and am now giving Anomaly a whirl in preparation for the sequel due to the x64 upgrade.
What are you guys playing?