Nice game, nice challenge, art is fine, the little square is cute. It needs some sound effects. I liked the parry system. The cannons need some feedback when destroyed because they simply disappear and I'm not sure if I'm destroying them or not. Also the diamonds need some kind of points text when grabbed so I know what value I get. It would be great to add more kind of pickups with different values, maybe powers to help you aside from the parry system and different projectiles to add variety.
Nice Job! Best of luck!