Finished this and still not sure if it was the acting, writing, or directing but something is definitely not right. That being said (keeping in mind that live action is its own art form and shouldn't be compared to the manga or anime), it's still a really fun and enjoyable watch. Once you get through the first episode it becomes easier to just sit back and enjoy the ride. Despite the flaws you will find yourself loving the characters (and the actors that portray them). Yes, they changed things and if you're a hardcore One Piece fan you might not like this as much as casual fans, but you should still give it a try. The special effects are done very well, they do an excellent job covering the back stories of the characters, And the essence of what makes One Piece, One Piece is still very much kept alive.

When it comes to adaptations, I always try to follow the philosophy of parallel universe:
Manga
Anime
Live Action

If they kept everything exactly the same as the source material where would the fun be in that?