This was one of my favorites. I was initially dubious of the mechanics, but once I got the hang of them (and figured out the quick turn button) I got really into it. I'm not normally that into these sorts of top-down shooters, but the gun kata element gave it just the right amount of depth -- there's an element of puzzle-solving and not just shooting, since you need to take a moment to line up the correct shots. The framing story was also quite funny, and I loved the pig noises on game over, since pigs are adorable.
The hardest level for me was level 5 (with the flying pigs). The introduction both of a much faster enemy type and the more limited movement space proved really tough. I agree with your postmortem that the game would have benefitted from larger screen/area sizes.