You should elaborate on the red/blue attack modes and shield compatibility more, even in the game description. I think it's a really interesting idea but it takes a while to understand. I think the blue shields are also rendered in reverse somehow on the first real level's box enemies, so I didn't realize I was supposed to hit them from behind.
Great execution of the theme, the rewind / ffwd mechanics look great and the enemies telegraphing their attack felt very polished.