I got the lens a couple of hours ago. It's raining buckets so I didn't take it out today, but I did a few shots around the house and tried to match a shot I'd done with the Zeiss 21mm a few weeks back. Lightroom doesn't have a lens profile for this lens yet, needless to say, so I used the one for the old 20mm f2.8 D and it's close enough for the moment.
So here's a shot of our kitchen, dining room, and living room, first with the Nikon at f1.8, and then with the Nikon and Zeiss at f2.8. The Nikon is a bit wider, but the difference between 20 and 21 is a bit more obvious than I'd expected. You can see that these shots line up pretty well on the right side, but the Nikon gives a good bit extra FOV to the left. I focussed around the faucet and flowers with the Nikon - I obviously was focussed farther back, maybe the dining table, with the Zeiss. Because the foreground is less in focus and the background much more in focus with the Zeiss. Sorry about that - I guess I didn't remember where I'd focussed a few weeks back and didn't check closely enough before I tried to replicate that shot today.
In any case, the Nikon isn't the Zeiss, but I think I'll be really happy with it. I like the size, weight, feel of the lens a lot - it's a lot better suited to the way I shoot than the Zeiss was. And it's quite sharp, even wide open, pretty good out to the corners. Probably not a good idea to compare it to a nearly perfect lens, but this is the only shot that will probably happen on...
Nikon f1.8