1/ It is much fatter/bulkier in the hand than even my F2. Yet it feels much less substantial than even my FM2n. It really feels like a cheap shell, not a high quality item. The Fuji XT-1 that is similar in intent feels much more solid.
Leica's digital M series cameras feel really solid. Almost like their film cameras.
2/ Unlike Leica's (and to a point the Fuji XT-1) clean design, the Nikon has edges/knobs/protrubances that stick into your hand everywhere. For this reason the D610/D750 are a much better design. They are pleasant to actually hold.
3/ The Nikon DF was marketed as being able to use the old MF lenses. Backwards compatible. It can, but its implementation is no different than any of the other Nikon DSLRs. The marketing babble pretended otherwise, but you get the same focusing screen as the other cameras. There is no 'real' screen for manual focusing. Focusing my film Nikons is much better and more accurate than manually focusing the DF.
Leica gets this right - I guess it is much easier for them as they never had an AF implementation - but Nikon had it right with their old film cameras. So why couldn't they do it again?
So you can see, for me, the DF is such a disappointment as it could have been so very cool. But the reality is that it is just a marketing gimmick and it has neither the handling, the build quality, or the haptics that it should.
If I am going to shoot my AIS manual focus lenses on a Nikon DSLR, I would just get a D750. The focusing ability would be the same, but I wouldn't have to deal with the pretense of the poorly implemented design.
I really wanted the DF to join my Nikon film cameras. I am so glad I opted to rent one first.