Back then we would talk about UI when we meant UX. The KPT plugins had a very odd visual design but the way that you could iterate patterns and processes on an image was unheard of.

People also look at the designs that the filters made and didn't think about how they could be used as selection channels and other ways of manipulating an image. Kai's original work was about using selection channels in Photoshop to create stunning effects and while you could use his tools to create a background or a texture they could also be used to manipulate the colour and tone in images in really incredible ways.