If you've played cuphead then you know the four stars speak for themselves but I do have a few issues with gameplay:

Parrying during aerial bosses can often make you lose health, particularly annoying if you're going for a perfect run

ms chalice's parry dash often knocks you up slightly after completion which can lead to you being hit

super arts have no invincibility frames meaning you can die the second you stop the attack

finally that knight boss in the king's leap is way too long and way to easy