About the growls/vocals that seems to turn most of the people off, I think it's very suiting to the internal conflict "Zero" must have had to go through after Zero 3's final boss fight when he has to choose when the truth about "Zero" comes out (hope I'm not spoiling anything there.)
Pretty sure if we got inside Zero's head there'd be some screaming anyways. I know I screamed a good number of times navigating through multiple death traps when I first played MMZ.
Anyways, I loved it. Off to play MMZ. Again. xD