I'd have to say that the G3 solved my only real issues with the Nexus 5:
Battery - the 5's battery is just on the small side, and I used some custom kernel functions, like dt2w that didn't help matters. I've noticed a significant improvement with the much larger G3.
Camera... The nexus 5 takes good pics and video, but I always fought with how quickly and accurately it focused. I have quite a few shots that are useless and a number of blurry videos. The G3 is a focusing demon due to the laser autofocus... Its no joke. That alone makes the camera vastly superior.
Yes, the Nexus is smoother and more fluid, but the G3 isn't all that far off (at least mine isn't) and more than makes up for it with the other functions that it excels at.
I worried that I'd get a healthy dose of buyer's remorse after switching, but a month later, I have zero regrets and no desire to switch back... The G3 is an awesome device.