I think they cast Uenoyama well. I'm OK with Haruki's casting. I'm still on the fence about Mafuyu, but Kaji is my favorite and I'm not thrilled with his casting.
I love this series because Sun is serious and quiet and always has a little wrinkle between his eyebrows from worrying about sky and speaks with no body language but Boat is funny and animated and always smiling in interviews and looks totally different (I know, acting, I like acting)
One of my top 3 favorite anime and Manga.