Diamond is Unbreakable was a really dang good part. It was fun seeing the series switch things up as far as the setting went. Instead of our heroes going on a journey to some place to defeat the main antagonist, instead everything was self-contained in Morioh, having them defend their town from threats instead.
Josuke is my second-favorite JoJo now. It isn't much of a surprise considering his dad, Joseph, is my favorite JoJo overall. He had a lot of cool team-up moments with other characters, my favorite being whenever he and Okuyasu would hang out, then him and Koichi and him and Jotaro. (Would have liked to see more interactions with him and Joseph.)
As a villain, Kira was great. Second behind Dio overall for me. It's kind of a shame that we had to get through two unrelated antagonists, Okuyasu's brother and Chili Pepper, before he became the prominent villain of the part. That was one heck of a final fight between Kira and Josuke though, and Killer Queen has to be one of my favorite stands now.
I'm looking forward to when Part 5's anime comes now. Should be interesting from what I've heard about it.