As others have stated repeatedly, the "look" of various UI elements plays a large role in usability, particularly when text is difficult to read and UI elements (such as buttons) blend together with backgrounds.Thats more complaining about the look. I happen to like it but thats just an opinion as is yours. Whats wrong with the OS though?
If we only cared about features/functionality, we would all be using Android. Android has always excelled in the features/functionality department while lacking when it comes to looks and usability.