It's the same size as a D610 or 6D (checked camerasize.com). It's a DSLR with a smaller grip, boxier angles, and 3 dials (ss, ISO and EV).
But wouldn't it play nice with the older D lenses, with apertures? So, you could go full manual.
Sure, the back doesn't look retro, but what do you want? No LCD?
btw -- it also has another feature. They dropped the video. Addition by subtraction???
DPR's summary from their initial hands-on
Nikon Df Review
"As such, although I hate to say it: from a cold, hard practical point of view, I can't shake the feeling that the Df is a little bit... silly. Hardcore Nikon fans will point to the support for 50 year-old non-Ai lenses, which is valid, but I suspect that the constituency of photographers for whom this is a real selling point is vanishingly small. Of course, I could be wrong. Naturally, there will be some photographers who will see the Df purely in terms of a lower-cost shell for the D4's very capable sensor, and might not care about the design. "