Has anyone made this transition?
I made exactly this transition except my G3 was on AT&T. The Nexus 6P is a much better phone in almost every aspect except maybe the camera. The G3 camera with OIS took amazing pictures. I haven't really used the 6P camera enough to compare but I doubt it's going to be a difference that matters to me.
LG software? I found just about all the LG software to be useless so I'm not missing it at all. The LG stock launcher was pretty terrible with that boxy interface on the main screen. I would always remove all of it in favor of HD Widgets. I never used the little widgets and apps that LG provided.
Speed? Of course any newer "flagship" phone is going to be faster than an old one. The 6P is blazing fast compared to my year old G3. It's all relative though. The G3 was still operating at acceptable speed before I sold it.
Battery? HUGE difference. Combined with doze, you are going to run a lot longer than the G3.
Stock? It's wonderful. None of the AT&T junk on the phone. I know Verizon loads up its phones with a bunch of cr*p too. So nice to have all of it gone.
Fingerprint reader? So cool! And so easy to adapt to because the G3 had its power button on the back and that's where the fingerprint reader is on the 6P. It was totally familiar to me.
I do miss the double-tap to wake on the G3. I don't like that I have to pick up my phone (6P) to unlock it. I was in the habit of double-tap then pattern unlock all when it was sitting on a table. I have also had to adapt to the volume keys in the traditional spot on the side of the phone, not the back. But - I'll get used to it.
The 6P is physically bigger than the G3. The 6P has bezels at the top and bottom to accommodate the speakers. That's something you have to take into account. I had told myself that I would never get a phone bigger than the G3 but here I am. It's taken me a little while to get used to the size of the 6P but it wasn't a huge jump from the G3.
Some people have talked about issues with Verizon's voicemail and the 6P on this forum. I don't know if that's still an issue or if it was cleared up. I use Google Voice so I didn't have to load any AT&T apps onto my phone.
Make the switch. If you are okay with the size, you won't even think about your G3 again.