Part 1 didn't really have much. At its core, whilst entertaining as mindless action, it was basically just a Hokuto no Ken knockoff with Dracula elements with the only thing allowing it to stand out beyond memes being the ending being unexpected for a Shonen (and in terms of shocking endings, Stone Ocean is far better and Ashita no Joe's ending stomps both).
Part 2 was when it started to come into its own and stand out compared to a lot of other Shonen at the time with elements such as having an active female fighter or reliance of tactics over brute force, though even here there were elements in dire need of improvement. Whilst Araki's way of killing off characters wasn't as melodramatic as Part 1's, it was still far from flawlessly executed in how the highlight death of the part had a lazy backstory infodump directly beforehand, which is the kind of lazy excuse for character writing and setting up a death I'd expect of something like Attack on Titan or The Walking Dead tv series. With the exception of one character death in Part 3, Araki didn't really become good at writing sudden, realistic deaths for main characters until Part 5. The tactics also could've used a bit of work, with many of Joseph's coming off as a little contrived or too luck dependant. Still a good way of expanding the story and giving it more of its own sense of identity, but it was clear Araki was still trying to find his voice.
Part 3 is where the series finally gained a solid sense of identity through the use of Stands and the necessity to further use tactics to overcome an enemy's ability. Its implementation could've been far better, however, as Araki was so excited to show off his new idea he completely threw Hamon aside beyond a select few uses despite it raising some very large questions such as why Joseph didn't keep up his training or why he or Lisa Lisa didn't pass on the teachings to any later Joestars such as Jotaro. Part 3 has its own large list of problems when it comes to writing, though when limiting it to just the evolution of the series, it did a decent job at providing Araki a solid sense of identity as a creator and help establish how he'd structure the flow of the series from thereon. It also works well if viewing the first 3 parts as a trilogy that was completed, given how the focus on Vampires and Hamon completely fades away with later parts.
Part 4 was definitely a major change in tone compared to the previous parts, and not just in how the art style gradually deteriorated from highly detailed manly men to slimmer characters and less shading. The more superficially mundane setting of a small town made it feel far different than the epic quests that had characters travelling across countries in later parts, yet Araki showed a good sense of confidence as a writer by making it work in terms of stakes through better character writing and more ambitious ideas, Kira's character as a whole being the prime example. In some ways, it was a step down, the main one being how there were no major character deaths from the main cast that was an iconic staple of the first three parts and would've been especially useful in allowing Part 4 to stand out from its Shonen peers when Jump series had become far less willing to kill of members of the main cast aside from JoJo after HnK ended. It can also feel quite disjointed compared to previous parts as a lot of characters with whole chapters dedicated to them such as Tonio or Janken boy didn't contribute anything to the main plot and just felt like filler (especially troubling when Tonio could've been a great asset to the main cast if they'd brought him to help fight Kira). Aside from those flaws that make it feel a little disjointed compared to its predecessors and successors, it was otherwise a great way of Araki showing his style as a writer.