I have played with the LG G3 a bit and I think even from that to this phone is an upgrade. I just think LG UI is counter productive, battery and performance draining. It's really a mess. That's the main thing you're upgrading to, a cleaner interface and software features that are very useful.
The camera will be a small downgrade possibly. The Moto X 2014 use the same Sony sensor as the G3, but Motorola doesn't do as good of a job tuning low light images, which was an issue with the original X as well.
Battery life 'may' be a downgrade. I am slightly concerned about battery life, but I still think base on past experience with various Moto phones, 3.5-4 hours of screen on time should be possible with this one, just because it had a big boost in CPU power and screen size from the original X, but the battery size stays nearly the same.
I think if you want a clean interface, with usual features that help simplify your life, strong radio signal and good voice quality (this thing have four microphones), and faster updates than any other non-Nexus phones*. Moto X is the way to go.
*Moto X did get updates faster than Nexus once, but it was a specific technical issue they had to fix. By an large, Nexus updates faster than anything else (which is why it's running Android L right now and not the Moto X).