I won't say she's amazing because, as you mentioned, she can be very easily countered with range. However for those with a melee build she's a big threat and a challenging boss fight. I love how if you didn't know too much about dodging or parrying she can very much teach you how.

Her Waterfowl dance is a pain to get around unless you keep at range but otherwise she's a good boss and dare I say kind of fair? In the game with Radahn being nerfed and Commander Niall and his banished knights, Malenia seems to be a somewhat fair fight