I am a fan of Naruto, One piece and I know the author. 3 in 1. Nothing the dislike. The author will not give up on a fic and he has a very stable release rate. He already wrote a OP fic so he has experience with OP and with the new Chapters recently on One Piece making so many revelation I believe he will be able to write an even better fic. good luck mate. But I know you don't need it.
The story is good despite some problems. The main issues that i see are how directionless the story is. After the whole Alabadta thing, it feels like the character is just getting dragged instead of moving the story. His personality also tends to switch from time to time. It had an alright start which good good during Alabasta but after that, i just suddenly lost interest. The MC isn't just that entertaining to read sometimes.
Man, it would be so good if the dialogue was better. everyone talks the same. they talk and over explains everything, King Cobra says "guys" like he's not a noble for Christ sakes. its painful to read, the characters should talk like they are separate people with different origins and upbringings, not like clones of each other. if it wasn't for that it would be a great for me.
it's written well enough, and there's nothing major inherently wrong, but many of the decisions made when merging the world's of naruto and one piece are just off enough to make it hard to enjoy. for example, the ways it's written makes the mc, hashirama senju, seem less like a si into the body of hashirama, and more like hashirama's grandchild that just happens to be named after him. not necessarily a problem, but the synopsis implied it was a si into the og himself.
Mostly just preference For the MC slightly didnt like his attitude in everything. Too much cuss words I think, I dont have a problem with that but using it too much lowers the quality of the story Weird out about relation of everything like why make hashirama and tsunade same generation like they both have siblings. With nawaki that the naruto anime doesnt have much info you can write many thing there