In the last couple of weeks my Pentium 3 PC with Windows 98 sees frequent use. I really like the austere desktop experience that Windows 98 brings to the table. But I can see how I sometimes yearned for a more attractive environment back in the 90s.
Back then I used to tinker with the built in settings to create bizarre color schemes. I used to spent quite some time on those tinkerings, only to revert back to default after a few minutes. The exception being some pre-built desktop themes. The ones I remember using for longer periods of time are the Curse of Monkey Island one and the 12 Monkeys one. Not only the graphics were nice, but also the sound effects. They are still available on archive.org: https://archive.org/details/theme_cmi_202005.