Crypt of the NecroDancer is an action rogue-lite with turn-based action based around the rhythm.
It's been in Early Access since the end of July last year, and after months of steadily growing content, the full version of the game is coming out on April 23~
Out of 2,341 reviews, 99% of them are positive. That is some insanely good stuff right there, and last I checked, that was second only to Half-Life 2.
Music by Danny Baranowsky, too! And the shopkeeper sings.
It's been on sale a few times, but it's definitely worth $15 at least. (Unless you really like complex game mechanics, I guess.)