My Verizon M8 just finished updating, too. It did take a long time! When mine got done, I got an error message that Google Play Services needed to be updated. I clicked the message and it took me to the Play Store. The only option was to deactivate Play Services, which of course it wouldn't let me do. I restarted several times, clicking the message each time. I tried doing nothing to see if a download would start. The download looked like it started, but would never finish. After several restarts (because the message goes away, and the Store couldn't be used), it finally updated.
Just an FYI...perhaps the site is overloaded with updates. Everything is fine now, but it was about two hours altogether before everything was finally done (including the Play Services update).