There are two different things here… iTunes was a one for all related to media. They split their functions, which I think was the smart thing to do, across different apps and the OS itself. Again, it had/has a lot of sense.
The problem here the function related to MUSIC, is inferior on the Music app to that part on iTunes app. Also, it's inferior to the equivalent app on iOS, at least on my impression.
Of course, if you are just playing music and not doing anything else, the app is probably fine. I'm not doing much either, but I'm also feeling that things are missing and the app it's a little bit buggy and not as snappy as it should be.
I, for one, much preferred the unified approach of iTunes. To be Francis, it's rather annoying to have multiple applications to perform the actions that one application—iTunes—used to accomplish.