Pretty tough
Well, at least the first time around. By the second time,you knew all the boss attack and movement patterns and it's far easier. It took me two times to get all the medals, and it got really boring the second time. You fight the same things over and over exactly the same as the first time.
The animation has a very unique style to it, and I kind of liked it, yet felt it's a little too warped for me. The music was pretty fitting for the game. For the character movement though, you tend to slide way too much and it's hard to control. Also, you only really needed to mash the S button through the whole game. Just saying only one attack button was really needed and the combos were not worth the effort to use.
Ok, here are some bugs. I found that when I was near full health, and was hit by the final boss, I was instantly brought down to no health. Now, this only happened once, but I was very annoyed. Also, when you fall through the floor, I actually fell through the SECOND floor. Now, this may have been because I had moved when falling. So I had to fight the last boss by jumping under him and holding A.
But, what kind of a game is perfect? I still think overall it deserves a 5/5 and 10/10.