Ok, so after been using iOS 8.4 for almost a complete day now, I must say that it's very very smooth. It feels much faster.
And one of the best things with updating to iOS 8.4 is that you get more free storage space. I actually got almost 1GB more free storage on my 64GB iPad Air 2. And around 700MB on my 64GB iPhone 6.
That's what I call optimization and progress! Nice work Apple.
It's too bad that third-party keyboards still crashes a lot though, but I got the feeling that it got a tiny bit better now with iOS 8.4. So hopefully that annoying bug will be fixed in iOS 9.
And it also seems that the restarting of the device that sometimes happened when I installed app updates from the app store has stopped. Finally. That bug was quite annoying too.
And the battery life seems to be a bit better too on iOS 8.4. I have used my iPhone 6 a lot now (just above 4 hours of usage time at the moment), and still has 59% battery left. To me that feels a bit better.
So all in all I'm quite happy with iOS 8.4 and can highly recommend everyone to install this update.
PS. I still haven't bothered with testing the new Apple Music and Beats 1. I'm not so interesting in that. I don't use my devices for listening to music. I use them for work and content creation. But I eventually will try it out sometime.