A bug: some of the toggle buttons are only two pixels tall when they are first unlocked, making them hard to discover. This includes the "Mode: TIME/AMOUNT" buttons, and the "Retry: ON/OFF" button in Settings. I first discovered the Mode buttons by accident, when I was trying to click "Auto Prestige" and was off by a couple of pixels! Then when I saw a thin horizontal green line on the Settings tab, I thought, "I bet this is another hidden button."
Too simple. The first 16 levels or so feel like a very easy tutorial. The remaining 4 levels are not really any harder, just longer. In a proper puzzle game those should be the first four levels, and things should get harder from there. As it is, the games few mechanics don't turn out to interact in interesting ways.
 "Synergism"){kind=icon}
 "DUMO"){kind=icon}
 "Icarus"){kind=icon}