Everything is overdramatic--from the choreographed movements within scenes, to the pure righteousness and pure evil of Jonathan and Dio, to the art style itself with its super-muscular men. It makes me think of what I imagine an opera would look like, everything exaggerated to evoke the base emotions and intentions of the story. A great example of this: We see Dio following after Jonathan at one point and choosing to walk vertically up a wall by jamming his feet into the wall rather than walk up a staircase which was literally right next to him. Was there any reason for his character to do that? Hell no, but it very clearly got across the inhuman level of physical capability which he had gained after donning the mask. And showed his complete disregard for social expectations. And it was funny.
And that's how the humor works in this manga. On the surface, everything is portrayed as being serious, but it's just so overblown and ridiculous that it creates a sense of absurdity. I do appreciate how this leads to some very uniquely odd fight scenes. Such as having Jack the Ripper flex his muscles to fire scalpels from beneath his skin where they had been burrowed. Or having JoJo slice Tarkus's arm in half, lengthwise. Or Dio squeezing the liquid from within his eyeballs at such high speeds that it acts as a projectile which pierces flesh and destroys stone pillars.
The first chapter starts out fully colored, then transitions to a grayscale with red tints. Most of the chapters are black and white, but sometimes this red-tint technique is returned to. The best part of the art is the inanimate objects, which are drawn excellently. However, the artist doesn't seem well versed in drawing emotions or very distinct facial expressions. And the body proportions are drawn badly. Arms and legs seem to be awkwardly attached to the torso, making characters frequently look stilted or resemble action figures.
The story, as seen through Dio's role: Dio, the childhood bully (ch. 1-5); Dio, the criminal (ch. 6-11); Dio, the fledgling vampire (ch. 12-16); Dio, the lord of zombies (ch. 17-40); Dio, the fated rival (ch. 41-44).