Usopp and Nami are pretty fucking perfect imo. Especially Nami. The Zoro guy has a little too 'cute' of a face for Zoro but that can be managed by the make-up artists and all. It's still a good choice. Some may not like Luffy but for me, this guy looks like he can indeed play the part. His smile is amazing, which is a key factor honestly. Let's not talk about Sanji...
Characters are important too thought, if they can't play the role as what we know from the strawhats, they get massively hated for it.
Writing case they just need to follow the manga, if they try to do their own script, they probably going to fall Apart very fast.
The live-action cast is out. Netflix tweeted it out accidentally and deleted it. I'm fine with everyone except Sanji, lol. That choice looks so bad, lol. Maybe he looks better with the hair and all, or so I hope. Usopp, Nami and Zoro are perfect. Luffy's cast is as good as it could get considering how hard it is to find a perfect match for him.