First and foremost, I play a game because of gameplay. If the gameplay fits me, I'd keep playing for hours more. If I really love the gameplay, I might replay the game again someday.
The second reason for me to keep playing is usually progression and stuffs to discover. There are couple games whose gameplay is ok but there are multiple stuffs to discover so I keep playing.
That's about it. Story isn't enough to compel me to keep playing. Art and atmosphere are never my reason to play any game. Regular updates and new stuffs won't matter if gameplay doesn't fit me.
There's no game which surprised me recently yet.