I am only impressed with the SGIIIs performance numbers. As far as the phone itself looks and the lack of updates to the screen, not so much. If Samsung is to base their next Nexus design on the SGIII, they need to do a few things:
1) Super Amoled+ Retina display with PLS.
2) 2GB of RAM. Might as well. It will show up in numerous phones later on.
3) Have the LTE radios combined with the CPU/GPU SOC. This should help some with battery consumption.
4) Definitely have the best GPU available unlike the Gnex.
5) No physical home button like the Gnex.
6) SD card slot
7) Cameras. You know what? More megapixels isn't the answer. Better camera hardware is. Better low light operation. Better shutter. Better lense(s). Anything over 5MP is overkill on a cell phone. Improve the hardware.
I'm sure I could think of more, but this is just what I came up with on the fly. The next Nexus should be king of the hill when it gets released and have the latest hardware specs. The Galaxy Nexus was a refreshed Galaxy II with an updated screen. The next Nexus has to be more than that.