>>545972651 and 2 share some DNA, but have different design philosophies. There was a deliberate push for rounder, softer, and easier to animate designs.
3 is kinda an exploratory game. The design philosophy, such as there is one, was just to make the designs more intricate, using the better colors and resolutions to make pokemon that the technology would allow.
4-5 have different styles, but similar grounding philosophy, I think.
This was arguably the period where pokemon design first became contrived; pokemon were designed to be pokemon, but is also when designs started being made to be "cool". Generation 4 is kind of a spattering between generation 1 and 2, while generation 5 is attempting to deliberately emulate old design.
5 stands out as this is the generation where starters started being designed differently. They haven't fully realized it yet, but shades of the "Masculine and bulky, Cool and sleek, feminine and cute" triad appear, along with these starters fringing on being characters.
6 onward all have to be taken with the understanding that they were made to exist in 3 dimensions, so all have more depth qualities and layering than older ones. Compare Cloyster, whose insides are undefined, to Toxapex, whose insides are fully visible and detailed. Starters are now characters. To an extent in 6, but definitely by 7, pokemon are also being deliberately designed to make merchandise easy to manufacture, and the "chipmunk face" has taken root like the fucking Digimon eye in designs.
Late gen 8 into gen 9, the jury is out. The merchandise theme is still going strong, as are the starter characters, but designs are often messy and outliers. More reflection might shed light.
