What I've learned in my own tests and experience (I have tested the Zeiss 50mm f2 MP, and the 100 f2 MP) surprised me.
The first surprise and my first experience was with the 50mm. I tested it against the Sigma 50 1.4 (not a canon lens, but well-regarded and comparable to canon's best 50mm options). When I examined the test images in Lightroom I was amazed by the extra detail visible in the Zeiss images. The sharpenss of the test images were about the same between the two lenses, I just got more textural detail in the Zeiss images. Very, very impressive. However, better IQ doesn't necessarily translate into a buying decision and after my tests I sent the Zeiss back and kept the Sigma. The Sigma had AF and is nearly 1/3 the cost.
The second surprise was spending a couple of weeks with the Zeiss 100mm MP. I thought it would eat my 70-200mm f/4L for dinner. But, while some shots from the Zeiss 100mm were outstanding, I discovered that the 70-200mm did extremely well too. The Zeiss 100mm shots were loaded with detail, but so were my shots with the 70-200mm. I feel that the Zeiss 100mm is great, but that my 70-200mm also has excellent IQ. In this case the IQ difference was not as obvious or pronounced. This translated into another non-buying decision regarding the Zeiss.
So, what I've learned from the combined knowledge gained from my own tests and the detailed reviews from others (especially Chambers' exhaustive IQ pay-per-view reviews)is that Canon's best work is in the telephoto range. Canon's best telephotos are outstanding imo. But, in the wide-angle to normal range the IQ difference between Zeiss and Canon (or Sigma) is more pronounced. So, I have no plans or interest in either the Zeiss 85mm or 100mm, but I am keenly interested in the Zeiss 21mm, 28mm, 35mm f2, and perhaps even the 50mm f2. Since I already have the optically excellent 17mm and 24mm Canon tilt-shifts, I'm presently overlooking the 21mm and wrestling with the decision to pick either the Zeiss 28mm or the 35mm f2. Eventually, I can also see a place for the 21mm in my bag, the presence of the TS-E 17mm and 24mm notwithstanding.