I just got the Canon 24 2.8 IS and the first impression is positive. Here are two pics I took with the Canon and the Zeiss 21 2.8.
They are both taken at f/11 and I tried to match the white balance and exposure as close as possible. I also cut a part of the Zeiss pic so they have a similar frame. Shoot RAW, imported in Lightroom and exported at 80% JPG.
Nothing else was done. Do you see the difference between the two shots ? Which one is the Zeiss shot and which one is the Canon shot ?