HTC One M8 doesn't boot up completely after Lollipop update
I had the exact problem after going back to stock then applying the OTA.  I had to reinstall TWRP (I used "fastboot flash recovery twrp.img" according to the instructions here). 

Then I just flashed another ROM from the SD card, which have gotten beeter since I last checked. I recommend Viper or Adrenaline 2.4 androidrevolutions.com/neo/ADRENALINE/m8/