Bought a few games from the Steam summer sale, and all of them are in my "Current" library category.
The House of Da Vinci is a really good, and challenging, puzzle game where you explore, surprise surprise, Da Vinci's house. Various kinds of puzzles, and I'm loving it.
Unravel is another puzzle game, a physics-based one. The player character is made of yarn, and that yarn is what you use to solve puzzles and get past obstacles. The visuals are absolutely stunning (yet I can run the game at max on my less-than-powerful PC!) and the gameplay is really fun. The puzzles get progressively more difficult as you get further. Highly comfortable to play thanks to full controller support.
Subnautica is so well-known that I won't say much about it. I'm not sure if choosing the survival difficulty was the best choice for a first playthrough -- I seem to be getting hungry and thirsty really fast -- but I'll stick with it. The world is super beautiful, although more than a little creepy especially at night. I haven't made much progress yet, and have no idea where to find most of the materials (well, except underwater obviously), but it's already been a lot of fun. Diving also feels refreshing due to the hot weather we're having in the real world.