Completely blew me away. The Introduction story brought chills to my spine (remember I know nothing about The Binding of Isaac, so have no idea how much was borrowed from that game. Judging by the steam page screenshots, the gameplay is quite similar) and the storyline of being a demon with human understanding was perfectly introduced: I immediately knew why I was playing the game, and what my character's motivation was.
The gameplay -- regardless of borrowing -- is totally intuitive and exciting, and just playing with the keyboard I took to it immediately, and had a blast, playing to the 'To Be Continued' message. I only got one of the powerups (crusher)
Bugs: The Intro fades to black, and ended there on Edge. I got past that to the gameplay on Chrome, but not sure how. English text needs some cleaning up in the Intro, but not so much as to remove the strength of the phrasing.
Summary: I loved it. Great job, this wins the Shackjam hands-down for me!