I'm quite happy with my G5 plus. It was a bit of a PIA getting it activated with Sprint, but that was on Sprint's side not Moto's fault.
It's an upgrade in every way over the G4 plus with the possible exception of the screen, which is smaller and seems a little less bright than the G4 plus.
The biggest area of improvement is battery life and the processor. I got 5 hours of SOT yesterday which is probably better than any phone I have ever owned including the old Droid Maxx or Droid Turbo. The phone performs flawlessly and I'd bet if you handed it to random people on the street 90% would never guess this isn't a $700 phone.
There are few software differences between the G4 and G5, and most of the few changes are for the better. I particularly like the one button fingerprint controls instead of the on screen buttons. It is a useful and non-obtrusive software modification that feels like it came out of googorola days. It took me about 4 or 5 hours to get used to it and I'm not going back. One software difference I don't like is the new active display widget which doesn't seem necessary, but I can live with it. I guess my love for the active display asthetic going back to the OG Moto X is why I don't like that change.
Overall, this phone is a fantastic value if not an outright fantastic phone in and of itself. Particularly at the Amazon prices.