Truthfully, I would give this an 8/10. I give it five stars on here to promote it, which it deserves.
It's impossible to make a live-action series as good as the manga. That's a fact. Before this, I predicted with certainty that this adaptation would be a disaster. Of all the worlds to successfully adapt, this was the most difficult, and yet... This was about as close as you could possibly get.
The shortened length is obviously going to hurt the character development a bit, so it's understandable if those who haven't invested in the original series don't get as sucked in as the longtime fans. However, the themes of adventure and friendship are universal, and the crew behind the Netflix series smartly made those themes front and center.
The characters, for the most part, are perfectly adapted to live-action. The only exception here is Usopp, who just isn't working. To be fair, his character didn't make much sense in the manga either, but his personality there is far more dynamic than in this adaptation. He needs a serious infusion of pep if the series continues.
The set design, music and visuals are all excellent, with the exception of some CGI fails, but that's to be expected.
This is worth a watch. I really hope Netflix agrees enough to keep it going.