In case anyone else suffers the same symptoms - a couple of weeks ago, my G3 started running really slowly (and possibly a bit hotter).
Booting from cold seemed to take a long time and the ui starred freezing temporarily on a regular basis.
I was waiting for an ota marshmallow update and hoped that would fix whatever was making it go slow.
I was wrong.
The other night, I was using it and the screen went bright blue and the phone then started boot looping. Sometimes it only got as far as the LG logo and other times it for all the way to the lock screen (on a couple of occasions I could get to the desktop and use the phone 'normally'). Every time it ended up blue screening and then rebooting.
Ultimately, it was dead and despite managing a full wipe, nothing fixed it.
As a phone, when it worked it was ok but cracking screen, poor call quality (only realised that when I got a different phone) and general slow downs (possibly related to overheating (and I could only infrequently increase screen brightness to full because of the warning about overheating) means that I think this phone has been fair rather than excellent.
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