Exchange and weaknesses of the bosses are really neat and creative mechanic, but nothing really indicates that you can switch between bosses mid fight, so it doesn't give me any advantage) Boss portraits are good but can't really see them in all beauty in gameplay from top down look(
And one more question.... why crab? I've rated a couple of games already and cant fully understand why so many crabs everywhere...
But becides that, beat all the bosses, cool game!