Well, I'm definitely enjoying this. I'm only up to level 5 right now - it's got me a bit stuck, and I'm sure I'll feel really stupid once I finally realize what I'm missing - but that's half the fun of a good puzzle.
But even only this far in, I have to say (after being reminded of the keyboard controls my bug report thread) - WOW, I'm legitimately impressed! I spend more time than I should complaining about controls in games, and how often developers use a mouse at the expense of the keyboard (side-scrolling shooters using the mouse for the unidirectional fire button being a huge pet-peeve of mine, as my post history will attest).
This is the type of game that would normally just be mouse-controlled, and the keyboard controls here are actually a treat. Way better than the trackpad for sure, and I think even better than my brief attempt using the mouse to test the game on another system.
Kudos on putting some real effort into the interface/UX!!
(although my one complaint on that front would be that I think help says z/x work, but I had to explicitly configure them first, only j/k worked as a default, but that's a minor thing, since they can be customized)