I'm going to say my favorite like the title of the thread says instead of hours
Well other than tf2 in order it would probably be
Hollow Knight (In the words of videogamedunkey, "a masta-piece of a game, and for your wallet.")
Overwatch (Another team based class based shooter if you think about it)
The Binding of Isaac and all of it's DLC because lots of mods and mayhem.
Celeste (Story + platforming is challenging + good music)