Actually someone in our family installed GEOS and I couldn't help think it looked pretty advanced back in [Edit: 1986/87). I'd not done Windows 1 or 2, saw only Ads for Mac but never thought the C64 could run a graphical desktop.
Watch out when you buy them though....the transformers are notoriously bad and could fry your SID chip pretty quickly! Always warm them up for a while and measure the lines before connecting it to the C64!