You have made some amazing technology. I now use a MacPro for work, and have an iPhone and an iPad at home. The hardware and OS of each is, with a few exceptions, beautifully designed and extremely usable. So what the *#&%$@ happened with iTunes?
When I say "iTunes" I'm not only referring to the desktop program but also the Music app on the iPhone. I don't even know what to call that. Is it iTunes? I don't think so, because there's another app called iTunes that's the store. This is problem #1: naming. Seems so simple, but is so confusing for some reason. It doesn't help that you have two apps with near-identical music-note icons. You can buy anything in the store: not just music but movies, books, etc - why not use a shopping cart icon?
Problem #2 is syncing. Honestly, it was a critically bad decision back when to make iTunes itself also the file syncing program. You should have just created a new "iSync" or something. Having an app that tries to do two totally unrelated things, and still make it seem "simple" or easy-to-use, is extremely difficult.
Because of problem #2, I don't sync iTunes to my iPhone. I only wanted a small percentage of my music on the phone, but couldn't figure out how to not sync everything. So I just manually copy over any music tracks I want. This has caused me problems in the past, like when I got a new phone and couldn't copy the music; I had to choose it all over again.
Also because of that, I create playlists right on the phone, not on the desktop. This is fine and the interface is generally easy to use. (Although it's funny that you have a "clear" and "delete" button right next to each other - see this screenshot. That's a pretty subtle distinction.) The biggest issue is that when adding songs to the playlist, it only gives you a list of all your songs in alphabetical order. It's not grouped by artist or album or anything, and you can't search it. This is problem #3, and makes creating a playlist more time-consuming than it needs to be.
Now we come to the heart of the matter. I have a certain playlist with about 150 songs, that I spent a long time creating and curating. Yesterday I added a few songs to it. When I went to reorder the songs, it wouldn't let me. It let me drag them to a new order, but when I went back to the playlist later, that order didn't save. It had reverted. Nothing I did would change the order. This is problem #4. It's a straightforward bug, but I couldn't find anyone else having the issue online.
Here's the worst of it. When I looked at the playlist today, it was gone. Well, it was still there, but it only had 14 songs. And a few were repeated, for some reason. (A-ha! Turns out, it only kept songs I had bought via iTunes. Awful.) All my work was gone. This is problem #5, a critical bug. And this same issue has happened before.
Problem #6 is that there's no easy way to save the playlist, or export it, or download a list of tracks, or anything ... or I would have done that as a backup. When you lose something, it's gone for good.
So, I'm done. I'm going to try out a bunch of top-rated music apps and find one I like that doesn't delete my data. I hope I never have to use the Music (iTunes?) app again.