Wow, it is quite nice. Despite the simplistic graphics, it is quite enjoyable. I love, that I can go back to previous rooms and I really like, that in the first room, there are only these target dummies, which teach me the basics.
There are some UX improvements, that would be great, for example, when I'm charging up my attack I don't want to look far away to see what my charge level is. It would be great if it was visible on the player and it started indicating immediately, that I'm charging, when I hold the button down. When I first started charging I thought that it didn't work, until the blue bar appeared.
Nice job with the game though :)