If you had the option to buy a poo cookie branded with the One Piece logo would you buy it? More importantly would you eat it? If you'd buy it then you'll most likely enjoy quite a bit of One Piece Unlimited Adventure, but if you wouldn't eat it it's hard to recommend for a purchase. You see while One Piece Wii is completely functional, it most likely won't be the least bit fun or engaging for anyone other than super fans. That being said, lets take a look at the fatty meat of the game in more detail.
It's a really good looking Gamecube game. *cough*
Essentially you're on one single island that's sectioned off. To open up new sections you have to find an orb in your current section and interact with it to see what items are needed to activate it. Then you go around beating the hell out of everything and anything including trees and rocks to make items appear. Once you have all the items needed you head back to the orb and activate it to unlock a boss fight. Kill the boss and you're on to the next nearly identical task. The only real variation throughout the entire game are slightly different sections of the island to conquer along with a small range of usable items that are needed to find certain orb unlocking items. It's all very basic and cookie cutter in nature and feels like something you'd find in a big animated movie game in the US.
The actual whacking of things to get items is also pretty bland as all you have to do to unlock new attacks is use your current attack over and over again until it levels up. The A button is your main technique which gets expanded into different combinations of A and waggling the Wiimote. There are quite a few characters to use and unlock but they all have the same button combos. The combos result in different attacks mind you, but it's the same action for the user.