I haven't had any problems with 8.4. Aside from a new music icon, it all seems like nothing changed. Except now my battery lasts more than a day like it did before 8.3. So I'm happy.
But, I have never launched / opened the new music app. It is of no use to me. So, perhaps the other iOS issues reported have more to do with the music app than iOS itself.
My logs don't show that music has tried to access data or use my battery. And aside from getting great battery life again, it feels just like 8.3.
For those who don't need music, I would propose closing the music app manually (force close) and then disable the music app in your settings (there's a setting for that). Then see if your other iOS issues clear up.
For those who need / want Apple music, you're at the whim of Mr. Cook. And likely they're more concerned with the money side than a few of us who dare to want it to work without glitches.
The old Apple is gone. It's been reincarnated into the quick to market and fast cash priorities of other has beens from the 90's. Too bad they didn't really learn why those companies failed.
I think Mr. Cook believes the brand name alone is all they need to be successful. But that fades over time when you consistently push out garbage.