I had a fun time playing this! Some of the mechanics are a bit inscrutable at first, but I really liked slowly figuring them out over multiple deaths. Haven't managed to kill what I assume is the "final boss" yet. The art is charming and completely coherent -- everything feels like it belongs. Though, at first, I didn't really notice the difference between floor tiles and the "void."
Also think I found a small bug -- I pressed Z to aim, but then pressed X to swap before shooting, and it jumped past the "reload" option. So I had infinite ammo for one rune.