Questionable quality and software support are the main factors IMO. When will we see 4.3 for it? The OG didnt get JB until months after the GS3, even though the OG didn't launch until the fall...months after the GS3 or One X.
LG is still a second tier phone maker.
My OG and Nexus 4 were two of the worst phones I've ever owned.
I've watched all the reviews on the G2 and it looks slick, but I'm not sure I would pick it over the GS4 or One, even with better specs. I'll buy it if its cheap though
I've handled the S4 next to the G2 and the G2 feels much more solid IMO, the screen is nicer as well, especially in sunlight, although I wouldn't say there was a big difference in screens other than the daylight visibility.
The updates do stink, but I plan on rooting and putting in a custom ROM so it's not a big deal to me.
I don't hold onto phones for more than a year usually anyhow.