I got a VZW G4 last Thursday and have been on it for work, and the off weekend days. I have had a few strange things happen that my M8 never did.
First off the touchscreen issue; Same as reported a few times, some touch just doesn't happen. I miss letters while typing, call hang ups, games, etc. Just a quirk that I hope they fix.
The On/Off/Home button: quite a few times the screen won't turn off, or on using the physical button. And a couple times if it does come on, the 3 bottom navigation buttons come on, but the screen stays black. The screen is on, but nothing....just black. I tried hitting the navigation buttons a few times and they glow for 2-3 seconds and nothing. I end up restarting the phone when it does that. 2 times so far I have had where the phone screen won't turn off with the button after multiple presses.
I have great coverage for the most part in SoCal with VZW, but at the in-law's house the coverage is horrible. This phone when dropped from coverage, then back on, the phone gives an audible "Verizon Wireless" Every 2-3 minutes. As far as I can find, there is no way to turn off that audible announcement. Super annoying, and I ended up just turning the phone off while I was at their house.
Quick Charge: I know that it isn't a QC 2.0 certified outlet, but I used my wife's S6 charger the first time charging up the phone. The phone then showed every 2-3 minutes "Your phone will charge faster with the original plug." I would dismiss it, and it would return. I can only guess that it is because it isn't QC certified.
A couple other issues, but no big deal. I don't recall having these types of issues with the M8 (unless I am blocking them out in my mind.) I liked the M8 and the UI but wanted a better camera. The wife has an S6 as I mentioned, and I just don't like the way it navigates. I will work with the phone and hopefully some of these bugs will get worked out soon with some type of update.