The complaints were that the UI was not customisable, with limited functionality, stubbornly did things the Mac way even if that was confusing to Windows users. The implementation was often slow and sometimes buggy.
But it had taste and attention to detail. It followed Apple's own HIG (design guidelines). The UI had some flashy details, but they had a purpose or at least didn't get in the way. I don't feel any of this in the current Apple designs.