Great concept, great art. The only gripes I have are the random difficulty spike (which someone has already commented on) and the controls. The controls issue may just be a me problem but sometimes I would move the wrong character and end up dying since my brain got the keys mixed up. I think this could be improved by adding a key to switch between the characters and control them individually rather than at the same time. I realise that this would make the puzzles where you move simultaneously unviable but I think it'd be a good trade for a better movement system. Just my opinion.
Loved it! Great game!