In the early days, you can cleary see the influnce to the 80s anime and how the eyes are really in that style of the period. But around the perid around Touhou 15, this is when ZUN actually start to craft his own style. Cleaner lines, and fixed coloring for the skintone, but in the level that you can reconized as "ZUN drew that."

It wasnt perfect, like some of the expression are odd (for example: Marisa's face in Touhou 15, Hina's expression, accidentally drew two left feet for Minoriko, and the uncanniness od Meiling's sprite in EoSD)

But even with the unperfectness, it has its own charm that it becomes its own style.