Mmm... thats quite hard... like best game ever and all... there are too many genres out there,
i cant pick just one.
If it comes to a game that i enjoyed a lot... well, i played Stalker Shadow of Chernobyl for 14 hours
straight... it was evening when i started... i lifted my eyes and it was dark already... walked to the kitchen
to get something to eat, came back and when i watched around me again it was midday already.
But when it comes to it... i guess that my fav PC only games are visual novels... i still remember
my first playthrough of Clannad so many years ago... i played for like 6 hours non stop and some more the next day and the next until i finished the entire thing. Addictive and satisfiying as hell.