I just got the G2. I love it. I was really set on getting an S4 until i compared them side by side in the Verizon store. in my opinion, G2 was better in every way. And it was cheaper at the time.
I got used to having the buttons on the back of the phone. I hardly use them though. The G2 has this 'knock-on' feature that i use instead (Tap the screen twice and it turns on). There is hardly a difference between the OS's on the Nexus 5 (4.4) and the G2 (4.2.2). I havent read much about what the differences are within the OS but i think it has something to do with creating apps or something. Im not really into that.
A lot of the specs are the same between the G2 and the nexus 5. Basically just a different body style.