The concept that LG has introduced (based on ideas that are still in progress, because they aimed to be a lot more configurable) is commendable.
The problems are that LG has admitted to the BBC (and others) that all the accessories are unique to the G5 and won't fit future phones. Not a massive problem, but perhaps a missed opportunity?
The camera add-on looks cheap and nasty.
The DAC is perhaps a bit too niche.
LG could have just gone with the removable battery and been fine, but upped the capacity and also had a smaller battery or capacitor to allow a hot swap without rebooting.
I expect the idea will be repeated, either done better on the next LG, or copied by another manufacturer.
Sadly I think the G5, hidden as it is in most shops amongst other phones, rather than being showcased like a Samsung or Apple phone, will sell in relatively low numbers.
The only positive is that if you don't mind the issues, in a month or two I am sure it will be around the £300-350 mark SIM free.
The G4, despite the lack of fingerprint sensor that I have to admit I now love on my Huawei/Google devices (and use to unlock the phone every time), is now under £300 and probably a better bet for many. The G4 camera is awesome, the phone supports 4G+, has a bigger battery and you can still change it.
The G5 seems to be a bit like Samsung's S6, and hopefully a disappointing glitch that will be fixed on the G6, as Samsung solved its issues with the S7.