Join Date:Joined: Sep 2006
I gave my G2 to my wife and bought the M8 for myself. I figured that if I decided within 2 weeks that I didn't like the M8, I could always get it back close to stock and return it (and get another G2 - or something else - for myself.)
To answer your questions:
No, I don't miss it completely - but I do miss some things: smaller size and "knock off" (M8 has knock on)
I haven't really noticed the difference in LED notifications, but I'm sure that it's something that can be worked around with a firmware and/or kernel mod.
I didn't consider it an upgrade.
For ME, the camera on the phone was only really ever a utility thing. I can still take pictures of stuff for reference (such as serial number labels, etc.)
Battery: The G2 battery is better than the M8 battery. There's no question about it. However, the M8 battery is still quite a bit better than a nexus5 battery.
Of course, that leaves the question of what is better about the M8: Better construction, MUCH louder built in speakers, HTC isn't trying to lock down the bootloader, sdcard (big deal for me and my 50GB of music), ability to easily convert to GPE.