I recently took the bold step and swapped by Canon 16-35mm f/2.8 L for the a Zeiss 21mm ZF. ZF means the Nikon version, so I attach it to my cameras with an adaptor.
This lens is very crisp corner to corner (the Canon zoom, whilst excellent, does soften at the edge of the frame somewhat). I love the colours and the rendering. I can't wait to use it at the coast during the summer!
This shot was about f/11 IIRC (the ZF lens doesn't report the aperture to a Canon camera) and I used 0.9 Soft Grad from Lee Filters to darken the sky.