Overall, it's a very good game.
I'm a big fan of the art, it's nice and simple without being abstract. Also I'm just a sucker for pixel art.
It's very difficult, I only managed to beat the first level and like half of the second one on casual mode.
My one complaint would be that you chose to give casual mode has less health. It seems a little too hard for a casual player to deal with dying after one hit, even with the more frequent checkpoints.