I never met a settings menu I couldn't whip into shape. In the G3's case, it just wasn't happening at an acceptable level for me. That and the S4 like stutter when scrolling pages or lists were deal breakers for me. I'll be very interested to see the G Flex 2.... but I'm afraid it'll be more like the G3 than the G Flex 1.
I fully expect the Flex 2 to be an incredible performing phone. 810 coupled with a 1080 screen should make for lightning crisp UI performance, I'd expect best in any class. My only concern with that SOC is heat... I've been reading a lot of problems with heat dissipation with the 810, but that might just be a question of working out some of the kinks in the kernel layer.
The G3's stuttering issues were mostly related to framework coding issues related to the higher res of the screen coupled with a massive UI overhaul that LG shipped with the G3. And we here in the US kind of got screwed since the international variant got a bunch of updates to the framework that hadn't (at the time) been incorporated into the US-model builds.... My G3 stuttered a bit and I went custom-ROM hunting to resolve it... when I loaded CloudyG3... which is based off the international model, the stutters effectively went away.... the difference was striking.... not the hyperbole "OMFGKERNEL100HOURSBATTERYLIFE" statements, but there was a obvious and drastic improvement in those mundane UI tasks that sometimes caused my G3 to hiccup.
But I knew it was a software issue. Yes, the 801 could use more power when pushing the QHD, but for 99.9% of the apps out there, the GPU performance is more than enough to run well. The AOSP ROMs were really fluid when they finally came out. So I knew it would be just a matter of time before they were fixed. And the Lollipop stuff would most likely be a lot smoother.
Software issues, FIXABLE software issues ain't no thing. I am not going to disparage a phone if there are some software tweaks to iron out, as long as they are ironed out.... and Cloudy answered that question. I am not a 'run stock' kind of person and I never saw a settings screen where I didn't try to push every button.... so "I had to go adjust the screen contrast" would never in a million years go into the 'Against' column.
The G3 is a kick **** phone.. with some adjustments that I, personally, don't blink at, it went from good to great. Nice screen, great in hand, excellent performance and a great and super reliable camera. The only real 'Con' I would list is a rear facing speaker. Didn't realize how much those suck until I got my Nexus 6 and heard the difference. But that's a small issue and most certainly not something that would drive me away.