I really like the G5, I chose it to replace a Nexus 4, almost entirely on the replaceable battery. I don't replace phones very often, and the Nexus was the only one I've had in years that didn't have a swappable battery (even back in my pre-Android Palm days!).
An easily replaceable battery, with offline charger, is just so much simpler as a way to keep your phone running than hunting for plugins, or carrying a charger pack. I've never understood why the majority of phone owners just don't get it!
I got mine SIM-free, and use a cheap monthly SIM-only deal (UK).
Anyway, I like just about everything about the G5, including the external SD card and twin cameras (not perfect, but I'm not a perfectionist in photography - I'd have a Nikon or Canon if I was). I even picked up a Cam+ cheap which does make the phone easier to use as a camera. But there is one glaring exception - GPS.
The GPS signal reception is really sub-standard, and I've spent a lot of time messing with it, even buying a cheap broken G5 to play at swapping parts. Fortunately the G5 is really easy to open and tweak (another of it's good points). I've concluded the GPS signal issue is a design flaw. The main antenna is actually on the front, under the screen top-right, and works perfectly if you run the phone with the back off. But bringing the metallic back within a few millimetres of that antenna kills it, obviously a design oversight. :-(
As a result there is an extra pressure contact on the antenna track that connects with a pad on the back, all looks very like an afterthought. It kinda works, but the efficiency of that extra contact seems questionable, and the signal is never as good as with the back off, and is probably very noisy so the GPS performance is erratic. I've improved things a bit with judicious use of copper foil and conductive glue, but it's still not good.
It's a great shame, and spoils what in all other respects is a really nice phone. Still, i'll probably be keeping it for quite a while.