I feel the same way. It's been going downhill for a while now... I think it started around 10 or 11. 12 is a whole new level of unusable, which really sucks for me because I'm fully invested in the Apple ecosystem.
There have always been haters, but I've been using it for 10 years and actually thought iTunes was great in the early days, and "good enough" up until a couple years ago. The new UI is just horrendous... I literally have to google how to do simple things like playlists... and then I forget and have to google it again. It's completely unintuitive, they've hidden some of the most basic elements of the UI.... arrghh... now you've got me started...
I'm open to hearing the alternatives. I already switched to Downcast for podcasts, and while not perfect, it's mostly been a relief. I've looked at some of the music alternatives, but having a difficult time finding seamless integration with both my Macs and iPhone/iPad. And I use an ATV3 for all my tv watching.
/rant