Super excited...mine just rolled in on the UPS truck.
I sold a very nice canon 24 1.4 II, to switch to this lens. The 24L was great at F2, this lens is even better.
This lens is smaller than the 24L, a tad bit lighter and takes a 67mm filter (vs 77mm). Based on the focal length, size, Zeiss color and contrast this is like a multi-purpose dream lens for me. I was reluctant to unload the 24L, but this lens tops it IMO.
If you look at the MTF charts for this lens, they look almost identical to the Zeiss 50MP. Pixel peepers have dinged this lens for being soft in the extreme corners, but the 50MP exhibits the same properties, and many people (myself included) consider the 50MP the best 50mm for EF mount.
I would say the only thing going against this lens is that it has some stiff competition from Canon and Nikon in their 24 1.4 offerings. I have no experience with the Nikon lens, but the Canon 24 1.4 II is a phenomenal lens. For the price, many will choose the AF and wider aperture of the Canikons.
The 21mm is also, of course, a great lens. Perfect for dramatic views and landscapes. The sharpness and contrast across the frame draws the viewer in to the scene. The 21mm FL is at times too wide for me as a "walk around" lens. Whereas 25 is perfect. So the 21 is my "landscape specialist" and the 25 is my "general" WA.