I've played this before in a previous demo day, I don't know if you had other playable characters then but regardless they were fun to try out. I don't think you had the shield boss either, that was also fun.
One criticism is that the bosses and enemies have low IQ, so there's no real challenge to the game. I also never really used other characters or special abilities. Brave's (the guy with the sword?) basic attack was enough to get through the game easily.
Only bug I ran into was both times I beat the stage boss, giant text would show on the screen that I couldn't read.