OTA update to Android 5.1 failed & wouldn't boot. It stayed on the spinning circles for hours. I tried clearing the cache, pulling the battery, removing the SD card, even a factory reset. If it had been a carrier phone or an actual Nexus device, I could have flashed a new system, but it's a Galaxy S4 Google Play Edition, so nobody wants responsibility for it. I finally bit the bullet and installed CyanogenMod. The phone works fine again, but the UI feels like going back in time a couple of years.