My Top 10 on steam.
Football Manager 2010
1,175 hrs on record
Football Manager 2012
1,058 hrs on record
Football Manager 2009
1,040 hrs on record
Football Manager 2013
932 hrs on record
Football Manager 2014
860 hrs on record (Play this lots offline and still playing 25 years into my career)
Football Manager 2011
840 hrs on record
Football Manager 2016
444 hrs on record
Football Manager 2015
320 hrs on record
Kerbal Space Program
277 hrs on record
Empire: Total War
146 hrs on record
As you can see, i like really 'boring' games