Design 2/5 : problem is, the visuals don't help. I've mistaken the bombs for bumpers after I discovered that the bulet could bounce at the walls and I tried to headshot the monster bc he was ugly as hell ^^
Theme 5/5 : nice fit with the theme.
Originality 4/5 : it looks a bit like mini golf to me but the addition of canons breaks this feeling so this is fine.
IMO, you started with the "feed the monster" idea and built the game around this. This is not a bad idea but you should have tried to simplify this into "get the ball from A to B using canons and wall bounces" and work more on the mecanics than on the visuals... I was honestly disapointed from the moving walls idea, it was really good and underused. Things like this are what could have make this game better.
Side note : I think you should try to make a neon / laser theme for the game, it will work great :)
Good job!