Man, some of those deals tempt me to buy them yet again, just because. So here are some deals I think is worth the playtime:

Spacechem -75% $9.99 => $2.49
Calling it a puzzle game doesn't do it justice. It feels more like coding your own thing from scratch. Also, seeing you solution move about is immensely satisfying.

FTL: Advanced Edition -75% $9.99 => $2.49
Solid roguelike which gives you the sensation of exploring the wonderous and deadly unknown.

Don't Starve Alone Pack -75% $24.47 => $6.09
Gothic and stylish wilderness survival roguelike with two DLC's.

Slain: Back From Hell -75% $12.99 => $3.29
Tough but juicy beat'em up. Got some negative reviews, but I think that was due to some crappiness that has long ago been patched up.

Card City Nights -30% $3.99 => $2.79
Really cozy and nice deckbuilder.

Alien Shooter 2: Reloaded -80% $5.99 => $1.19
Shoot monsters. Fun!

Submarine Titans -76% $4.94 => $1.19
Okay, never played this one, but ... it's an underwater RTS! I had to mention it!

Mmm, alien/zombie shooter 1/2 are great games. Shame the first alien (and possibly zombie) doesn’t run correctly nowadays, crashes and such like. Could do with an updated engine. I know they did start one, but it’s only the first 10 levels.

Ghost of a Tale (50% off) - I already recommended it a few times, and I will keep singing its praises at every opportunity. It's not for everybody, but if you like a fantasy story with charm and fairy-tale like quality, if you want to live an adventure out of a book by Tolkien or Lloyd Alexander (with some Brain Jacques flavor) this is the best game you'll ever find. It's absolutely gorgeous to look at, with fun stealth/adventure/RPG gameplay full of exploration, but most importantly it's just a master class in worldbuilding. With great characters, phenomenal mood, incredible attention to detail, it makes a small adventure feel huge, and it skillfuly builds a sense of a big, living, magical world that you only see a snippet of, but totally believe exists in its entirety. To me this is The Hobbit of games (and I'm scarcely capable of higher praise). And I just hope we will one day see its Lord of the Rings.

https://www.gog.com/game/kingdom_come_deliverance_royal_edition

"Only" $10 off, I know, but imo this game is worth beyond full price. The immersion factor is off the charts if you allow yourself to get lost in its world, and the game is absolutely gorgeous. More "indie" games like this, please! This game beats the pants off AAA releases, including Skyrim, for me.