Although I have had some relatively decent success in the Mutsuki and I don't think it's by any means a bad ship, it's definately not as fun to play as it's predecessors. The issue lies with it's weapons, the guns are meant to be a bit crap as they are with most other IJN DD's. It's nice having the increased flexibility that 10km ranged torps gives you but lining up a target at say 8 or so kms that has no obvious cause to change direction anytime soon but does just that, the second you launch the torps and then have you waiting a good minute or so until you can try again. That's where the fun aspect takes it's beating.
It's just up to WG to find an alteration that doesn't send the ship hurtling to the other end of the spectrum.