It may be only tangentially related to the genre, but Factorio has stolen far too many of my hours and is definitely worth the $20. It is engaging and challenging like no other game I've played in the past couple of years.
One thing I love about Factorio (aside from everything else), is the pricing model. It never goes on sale, and never will. That means the usual agonizing over "should I buy it or wait until a sale?" is non-existent. More developers should adopt that model.
I'm betting it will one day. I'm waiting.