One of the things that keeps Jojo's fresh is the slight shift in premise and genre that comes with each season
Part 1 started us off with a manly Hokuto no Ken (Fist of the North Star) style adventure mixed with horror, with references to more traditional supernatural things such as vampires and werewolves. Part 2 took that to the next level with the pillar men Indiana Jones style in an action-adventure, and pushed the hamon energy premise to its peak. Part 3 switched to the stand abilities, and made it into a road-trip/around the world in 30 days type story. And now part 4 became a mystery/crime drama.
I loved Part 3 (well the second half in particular) a lot, and also rated it 10, but if I were to name a weakness it was the fact that the story was a little disjoint. A lot of the enemies faced in Part 3 seemed pointless, almost as if they were put there just to extend the story. We all knew what the end goal was, and yet even though it felt like they should have arrived half way through, it took another 24 episodes. But it more than made up for it in good writing and excellent characters.
Part 4 doesn't have the same strength of characters Part 3 has. They're very good, but they're not great. But in every other field it shines with flying colours. The pacing, the art, the voice acting, and more were all spot on, in my opinion. Moreover, almost every episode advanced the story. I'm sure you could cut out around 3 or 4 episodes (roughly 10%) and it still would have been great. But it wasn't as drawn out as Part 3, where you could easily shave off 30-40% of the series and tell the story perfectly.
So to summarise my scores:
Story - 10. Well paced, easy to understand yet intriguing, well executed twists and turns, and satisfying ending.
Art - 9. There was the occasional part that seemed lazy, but most of it was masterfully and lovingly executed as usual, in the old fashioned style. The colours and special effects were very well done.
Sound - 9. Music, sound effects, voice acting - all very well done. This is one area where I think Part 3 deserved a solid 10, and I couldn't justify giving this the same score as Part 3.
Character - 8. This, in my opinion, is the part's weakness. Most of the main characters were great, but the chemistry between characters didn't match what was there with Part 3, or even Part 2. Although part of this is the nature of the genre chosen for this part.
Enjoyment - 10. Easily, unlike in Part 3, there wasn't a moment I was bored or feeling like the story was dragging on for too long.
Overall - 10. If I could give it a 9.5, I would, since it isn't perfect, but it's damn near close. Favourite Jojo's so far.
