Full review will be coming in the next few weeks. These compares right now are quick analysis I use and compare the two lenses. Please see Compare #1 and Compare #2 posted earlier.
Compare #3 looks at focus shift. For this one, I set both lenses to f/2, shutter to 1/180 second, ISO 160 and a distance of about 1 meter. In the viewfinder, the focus looked identical (to me) and I made no adjustments for focus shifting like in previous posts. Above is the Leica version, spot on. Below is the Zeiss. Of course, both are SOOC once again.
First thing to notice is the focus being off in the Zeiss. What looked dead on in the viewfinder is in reality off in the result. This is easy enough to overcome by knowing how much to back off on the focus, but something I wanted you to be aware of. Note: The Sonnar is optimized for f/1.5. There is no floating element in the Sonnar, so at f/2, you get the resulting shift in focus.
Notice the 100% crops below:
Next, look closely at the beards. See a little purple fringing on the Zeiss? Yeah... but you can correct for that as well - but again wanted you to be aware that this can happen in certain situations. Really, it can happen with most lenses as far as I know.
Finally, here's a slightly adjusted version of the Leica Summilux shot, so you can see what a not-so-SOOC image looks like. I didn't bother with a Zeiss version here since the focus was so far off.