For me is just annoying small issues like when I listen to music and get a notification from another app suddenly the volume doesn't go up as high anymore and stays low until you reboot the phone. Or that when I'm on Bluetooth it will mess with the wifi and you need to disconnect and reconnect to make it work.

I also really dislike (maybe this is just me) that I can't deal with files as files on an iPhone. I can't just move an mp3 or an ebook to the memory, find it via an app and open it. It feels so locked it.