(deleted and reposted this comment since I think it ended up in the wrong place first)

but I really like Zoro's barking laughter and the only signs of amusement we see from our swordsman from this point onwards are mostly just devilish smirks :(

I agree! I don't know if it comes from the fight with Mihawk or if it's more about the stakes getting upped more for the whole crew after they get into the Grand Line, but it's sad either way. Early Zoro's guffaws were great. Sometimes I wonder if he takes it on himself to be more serious so that other members of the crew can afford to still be careless (particularly Luffy, but also Usopp).