I've been playing Unturned on Steam a lot. They recently added a large Hawaii map which has been pretty awesome, with caves and ships and other stuff to explore. It was the only game I cared about when I left Windows a couple years back and it has run reliably for me even with integrated graphics on my Haswell Celeron. More recently I added a GT 720 that I had laying around and that helped make the experience better.
For a one man show, that game has improved immensely over the years. I played free for years and finally got the gold upgrade as a 'Thank You' to the developer. I really want to see the list of Linux games continue to grow, so I have been trying to throw down cash on games through Steam that support Linux.