Alright, I had the exact same issues as everyone else. I have had iPods / iPads / iPhones for a while and also have developer account, just mentioning that as a context because Apple needs to be aware that iOS 8.4 is very sensitive. After getting what everyone else above and below reported, namely, my iPad started freezing during Podcast playback, I attempted a restore. Then, every time I tried a restore it failed. I even tried to roll back to iOS 8.3 - epic fail again. Here is what I recommend for anyone still having trouble.
1) Disable OS X Firewall, 3rd party firewalls, router firewalls, etc.
2) Unplug all peripherals (USB hubs, cd/dvd drives, flash drives, etc.) and do nothing else while restoring.
3) Accept doing a clean install and losing "backup" information as it just won't work well
4) Force restore by Briansyddall method above
5) Restart computer after doing step 2 above, and then plug iPad directly into machine
6) Click Restore & Update (Again, ONLY the device and iTunes running - NOTHING else until finished)
7) Manually add apps and change settings, do not use back up file
I literally worked on my iPhone and my iPad mini A1454 for 5 hours before I read through all the error codes posted by Apple here that made me try step 2 above. Once I did step 2 and 5 together, it restored perfectly the first time. So, tying this into what I said above, that I have had many iPads, iPhones, iPods, etc., the point is that it seems iOS 8.4 is very sensitive to firewalls, sensitive to peripherals, and sensitive to 'upgrading' versus clean installs, hence the issue in the first place. I would be surprised if the above did not work. First time I ever had to do this even with developer upgrades, etc., ...
Regards,
Haack