GOG.com is bidding farewell to it’s Big Sale so that Summer Gaming can begin, the DRM free sale ends on June 18.
In regards to the sale, if you spend the equivalent of $5 you will unlock Sunless Sea, while RIME! will unlock after spending $20, that’s good value right there.
As for discount highlights. You can pick up XCOM: Enemy Unknown with 80% off, or maybe Kingdom Come: Deliverance with 20% off is more your thing. If you prefer your RPG. A bit more fantastical (but still just as white) you can get the Witcher 3 Game of the Year Edition at 60% off.
It might also be an idea to back up some of your Steam library through GOG seeing as Steam will no longer support Windows XP or Vista starting from 2019.