Omikron: The Nomad Soul, 1999's futuristic and highly complex action-adventure title, is now on GOG.
Ubisoft's huge GoG catalogue is 60% off this weekend. There's bound to be something in there for pretty much everyone.
GoG launches a pay-what-you-want Divinity series bundle with an advertised value of $32.
GoG's running a huge sale on retro Activision titles this weekend. I'd recommend picking up at least Arcanum.
If you're looking for a challenge, you can now pick up the remake of oldie-but-goodie La Mulana from GoG.