On a rating of out of 10, this star rating would reflect an 8/10; and as a long time fan of One Piece with some medium understanding of the different mediums, e.g. manga, anime, live action (you get the picture), this rendition of the story holds pretty strong for a live action adaptation.
Realistically, none of the manga/characters can be fleshed out exactly as their 2D counterparts. Therefore, in terms of the live action cast, I think they worked pretty well with the material they've been given, with some stand out performances from Emily (Nami), Iñaki (Luffy), Jeff (Buggy), and to some degree Morgan (Koby). Tbh, I can't fault much of the acting of all the cast; rather I would nitpick at some narrative and directorial choices made in some sequences. I think there were some scenes that could have been improved slightly with a different choice in approach, however, overall, there's not much I hated in this live action. Considering it's with real actors, on a mostly real set, it almost felt old school film making with heavy focus on the story and character, albeit a bit ham fisted into 8 episodes. Regarding dialogue, it's a bit cheesy admittedly, however, again packing all the bright gems in 8 episodes... plus considering it's based on a shonen manga, it'll do. A lot of the delivery doesn't feel cringey at all, and that's again down to the actors and the scenes they've been set up in and that's a positive thing! My partner and I binged the whole 8 episodes in one day 'coz we enjoyed it a lot! It was a solid 8 for me and it hadn't faltered. Now I'm rewatching with the original Japanese VAs.