Really nice! Visuals and sound were a perfect fit and the gameplay was simple and easy to get used to. My only criticism is that Knucklehead seems to slide backwards after attacking, as if he was on ice. It wasn't that big a deal but I did notice it more when I was fighting the boss. I had to constantly walk to minimize the slide back.
Overall it was quick, fun to play and well executed. It's a bit short, but that just means that I wish there was more because I had fun playing.