I own a lot of Canon "L" glass for my 5D MkII and 1D Mk III, and I love Canon lenses for their optical performance and swift auto-focus... But...
The Zeiss 35mm f/2 Distagon T* ZE is by far the most pleasing (and rewarding) lens in my bag.
I started researching lens performance (beyond sharpness) when I discovered the magical rendition of "contrast" with Leica lenses... If you look at a Leica photograph there is something EXTRA to the way it sees the world. I wanted to capture that "magic" too, but their is no way I could make a Leica my primary camera system, it was simply beyond my budget... Now, there is no way that you can equate this $1000 lens on a Canon to a Leica M9 and Summicron f/2 lens, but this is as CLOSE AS IT GETS (For about $9,000.00 less than a Leica system)! Until I can afford a Leica, THIS is my work-around.
The Zeiss 35mm f/2 Distagon T* ZE delivers exceptional sharpness (edge to edge), but it is the contrast and color rendition that make this lens a superb piece of glass... It's truly a lens with character. It's hard to get that character in Canon Glass (except for a few $2000 "L" primes, like the 85mm f/1.2).
Part of the reason you get a better photo with THIS lens (Or with a Leica for that mater) is that it takes extra time and care to shoot in manual focus. This care aids in your composition and in your determination for a great shot. Of course, if you stop-down the lens to f/11 or f/16 it's easy to "shoot from the hip" and "zone focus" using the distance scale printed on the lens, and a 35mm is perfect for street photography. But, it's the shooting at f/2 that delivers that beautiful shallow depth of field and dreamy bokeh that I was looking for in a standard to wide angle lens.
I have used this lens for landscape and location portraiture work with great results. I would NOT recommend this lens for fast focus work like journalism, sports, or birding (Unless you are comfortable with zone-focus style shooting). I would recommend this lens to a camera aficionado or perfectionist in optical rendition for it's superb character and manual focusing quirkiness.
HERE IS AN IMPORTANT TIP: Since the ZE lens is a Canon mount. On your Canon camera, use the back "AF-ON" thumb activated focus (instead of the half-press shutter button focus option in the set-up menu). While pushing the "AF-ON" thumb button, rack the manual focus of theZeiss 35mm f/2 Distagon T* ZE until the red-square and/or "beep" signals that you have achieved sharp focus thru the viewfinder. Using this focus method resulted in 100% critical focus for me, without the added expense (and disadvantages) of a specialized after market focusing screen.
Or when ever possible, use the "Live-View" function to pull critical focus while working with any manual focus lens. (Let's see a Leica do THAT!)