THE BEST MUSOU. The action is incredibly fast and carries a great deal of satisfaction - very little regard has been given to difficulty (even on Hard More). Kizuna Rushes, Special Attacks and overpowered super-characters designed solely for the purpose of racking the kill counter as high as possible - it's not unusual to break 5,000 KOs on a single map.
The story mode does a fairly decent job of retelling the events of the entire One Piece saga, though I really wish they had waited until Dressrosa was over - so many great characters and special attacks from that arc are missing.
A must-get if you're a One Piece fan, and a should-get even if you just like musou action.
COMPLETION: Finished the Story Mode and got ~50% completion in Dream Log mode.