I think it was because it was ahead of its time too. WB 1.3 on my A500 was what impressed me the most, it could do amazing things at the time and was a much better UI than Windows 3.1 which came years later, plus it multitasked a lot better. Later on, my friends A1200's didn't impress me quite so much, it was still good but not as groundbreaking.
When I got my first PC I thought Win 3.1 was rubbish compared to my Amiga. They even had 2.0 at my college and that was unbelievably bad.
Windows 95 changed things a lot though, they finally got the UI right, and although you could tell it was still an OS bolted on top of another, I thought it was pretty good from a usability point of view. I'm not convinced a lot of the changes they've made to the Windows UI over the years have been good. I think the UI peaked with Windows 2000 myself.