Hearthstone. Requirements are so low it exists even as mobile app.
Two finger death punch
Cossacks Back to War
World of Warcraft.
I've been playing Civilization IV on my Surface Pro 3. It's destroying my marriage, my children's upbringing and my career. It's ok though because I can stop when I want to.
Telltale games, their games have low system requirements and still modern.
On pentium e5200+g210+ 2 gig of ddr2 ram
League of legends
Stardew Valley and FTL. I consider my Surface Pro 3 as a Potato, intel graphics and such.
FTL, avaliable on Steam. Great game.
Super light and super fun : Hotline Miami 1 +2 and the somehow similar Serial Cleaner.