What are your issues with the iTunes UI? I find it laggy, but I use the majority of everything in it.
very laggy, blue screen of death color scheme, doesn't save your place, no personalization in store except for there recommendations, refer to the tool bar for certain screen changes, etc...
the most important is the flow of it. hasn't been there since 10.7 IMO. It seems iOS 10 music is the direction there going and migrating the two or transitioning to apple music. which is looks first then UI. i want UI first then looks.
steve jobs had a passion for music. he understood the feel of good music, not just the sound. he incorporated that into iTunes of old. and thats why many got on the apple train. it was the simple feel good interface of apple, which i think is fading away.