This has been the first iOS 8 update that took my phone back a step. Things had been relatively crash-free and smooth since at least iOS 8.1.1.
But, now I've had Maps crash 3 times while using turn-by-turn navigation. Restarting the app, and even restarting the phone would simply crash the app again when I try using Maps. The only way to cancel it out is to instruct Siri to find another destination, then Maps works again.
And yesterday, the traffic indicators disappeared. Tried toggling the show/hide traffic button, and restarting the Maps app. Only after restarting the phone did the traffic data reappear.
The Music app is simply a mess. Very clearly, the app is trying to shoehorn two different agendas into one interface, and it leaves a lot to be desired.
The radio function in particular does not work for me at all. In the old version, I had my iTunes Radio stations arranged in a certain order so that I could use them like preset buttons in the car without taking my eyes off the road. With the new radio function, my user-defined stations only appear in the "Recently Played" section. The text and art are tiny and unreadable from afar, and the stations now appear in a different order every time I use the Music app. Not very safe to use in the car. There's no way to preset favorite stations or set preferences so that my stations don't switch places constantly.
Updated my 5S to 8.4 from 8.3. No issues so far. Surprised to find 500mb of space was recovered after update
That space recovery comes from clearing out the caches when the phone installs the OS update. Most of this space will inch back as the caches rebuild.
Another thing to check is your "Other" directory. If you use iTunes Match or have a lot of downloading activity, there might be a lot of garbage data sitting around the device. The only way to get rid of a lot of this is to restore your device as new. Once you do that, then restore the data and apps from a backup. If you want to keep your messages and certain app data, then you should do this using a wired connection to iTunes.
Because I use iTunes Match, a lot of junk data builds up on my phone. I restore my phone about once every other month as regular maintenance, and each time I will typically recover over 2 GB of storage space.