To answer the OP, G2 high-ISO IQ should be as good as current m4/3 offerings. DXO ranks the GH1 highest, but they haven't posted G2 results yet. I don't think we've heard any real head-to-head results yet. I've played with the G2 and high ISO looked a little better than my G1, at least as good as my EP1.
So if Nex is 2 stops better than the G2 in RAW, it should be 2 stops better in RAW than most other m4/3 cameras. That's pretty compelling if you shoot in RAW, and like the rest of the package. If you shoot JPG, sounds like Nex JPG output isn't spectacular.
As for UI, they can be funny things, with individual experience hinging on what we're used to and what we want to do.
I've only briefly played with Nex 3/Nex 5 bodies, found them both better than I expected but still frustrating. Part of the frustration was design, part was just unfamiliarity.
I shoot most often in aperture priority, and need to do 4 or 5 things often, so I want to be able to do them easily and fast:
1. change aperture
2. bias exposure
3. change ISO
4. tweak white balance
5. magnify finder (when using legacy lenses)
I found aperture/exposure bias control easier than expected on the Nex. Just turn the wheel. I forget what you push to toggle between the two, but it was easy; maybe just click the wheel?
That said, I find a horizontal control wheel, like on the Panasonic, easier to use then a vertical wheel, like on the Nex and Oly Pen. I turn the vertical wheel too far and accidentally click it more often than the horizontal wheel. It also bothers me a bit that the aperture/exposure is overlaid on the image. I'd rather have it outside the image area.
It's at ISO/WB that I hit a wall. No dedicated buttons on the Nex. Maybe I hit Menu? Maybe I hit one of the two unlabeled buttons? Then I wondered why Sony would have unlabeled controls, especially on a camera targeted at non-technical beginners. Didn't see a screen prompt.
At that point I shrugged my shoulders and surrendered the camera. I'll be more interested if/when a Nex 7 with more buttons debuts. I also don't think I'll buy any Nex unless they make one with a good eyelevel EVF. I have trouble using my EP1 outdoors, and mainly bought it for indoor use and video. I'll eventually sell both my G1 and EP1 and replace both with a G2.