It’s true.
After a loong time of teasing, Nikon has entered the mirrorless market with not one, but 2 models. Full Frame! 45.7 MP and 24.5 MP (above photos are all Z7 model)
Before getting into some of the specs, let’s talk about some of the Nikon legacy that you need to know with these cameras:
Your DSLR batteries will work! Not sure yet about the battery life, as most mirrorless cams use more juice (EVF and whatnot)
look like a familiar shape?
There is an adaptor, available timing as the Z7 model, so you can use your F-Mount lenses! That alone is massive. About $250.

with a lens:

Image stabilization? BUILT IN! I’m curious to see how that affects the older F mount lenses.
Silent operation? you bet!
There is a dial and an LCD info screen up top, as you can see

Have now learned to hate having to go into menus, for fast operation, and this is a help. Customization of buttons will most likely be the order of the day.
Yes, Wi-Fi and Bluetooth
External mics can be used AND you can use headphones on the body
Autofocus is Hybrid phase-detection/contrast AF with AF assist

How much you ask?

The Z7, avail Sept 27, will be comparable in price to the D850 at about $3400, the Z6, avail late Nov. will be about $2000. Both prices body only.
Remember: If you are a Nikon user, you already have the glass and the batteries!
One thing that must be mentioned: Nikon has decided to go all in on XQD media cards. Yep, one slot and new cards.
Word is hat there will be some updates that will allow for CF Express cards as well.
That will be an investment, although they are the faster cards that SD.

there you! a first look at the camera(s) There are 2 models with a primary diff being MP

Once this camera is on our hands, we’ll give you a better assessment.
Nikon, you did good!

the official word:
NIKON INTRODUCES THE NEW NIKON Z MOUNT SYSTEM, AND RELEASES TWO FULL-FRAME MIRRORLESS CAMERAS: THE NIKON Z 7 AND NIKON Z 6

MELVILLE, NY (AUGUST 23, 2018 AT 1:01 A.M. EDT) – Nikon Inc. is pleased to announce the release of the full-frame (Nikon FX–format) Nikon Z 7 and Nikon Z 6 mirrorless cameras, as well as NIKKOR Z lenses, featuring a new, larger-diameter mount to enable the next generation of ultimate optical performance.

The new Nikon Z mount system is comprised of mirrorless cameras and compatible NIKKOR Z lenses and accessories. This system has been realized through the pursuit of a new dimension in optical performance. It has inherited Nikon’s tradition of quality, superior imaging technology, intuitive operability and high reliability, all innovated from its digital SLR cameras.

At the heart of the Z mount system is the new, larger-diameter mount, which unlocks further possibilities of lens design. The Z mount system will offer a variety of high-performance lenses, including the fastest lens in Nikon history, with f/0.951. Additionally, the new mount adapter will enable compatibility with NIKKOR F mount lenses, adding to the range of choices for photographers.

Z 7, Z 6 Product Overview
The Z 7 and Z 6 are equipped with a new backside illumination Nikon FX-format CMOS sensor with built-in focal-plane phase-detection AF pixels, and the latest image-processing engine, EXPEED 6.

The high-resolution Z 7 has 45.7 effective megapixels, and supports a standard sensitivity range of ISO 64–25600. In combination with NIKKOR Z lenses, the camera achieves an outstanding level of sharpness and detail, all the way to the edges of the image.

The versatile Z 6 is an all-purpose FX-format camera with 24.5 effective megapixels, and supports the wide sensitivity range of ISO 100–51200. With superior performance at high ISO sensitivities and full-frame 4K UHD video capture with full pixel readout, the Z 6 responds to a variety of needs, such as shooting in dimly lit environments and high-quality movie recording.

Primary Features of the Z 7 and Z 6
1. Equipped with a new backside illumination Nikon FX-format CMOS sensor with focal-plane phase-detection AF pixels
The Z 7 and Z 6 are equipped with a new backside illumination, Nikon FX-format CMOS sensor with focal-plane phase-detection AF pixels, and the latest image-processing engine, EXPEED 6. The Z 7 has 45.7 effective megapixels, and supports ISO 64–25600 range of standard sensitivities (reduction to the equivalent of ISO 32 and expansion to the equivalent of ISO 102400 is also possible). The Z 6 has an effective pixel count of 24.5 megapixels, and supports a broad range of standard sensitivities, from ISO 100–51200 (additional reduction to the equivalent of ISO 50 and expansion to the equivalent of ISO 204800).

2. A fast and accurate hybrid AF system with focus points covering approximately 90% of the imaging area
The Z 7 has 493 focus points2 and the Z 6 has 273 focus points2, enabling broad coverage of approximately 90% of the imaging area both horizontally and vertically. This hybrid AF system uses an algorithm optimized for the FX-format sensor, to automatically switches between focal-plane phase-detection AF and contrast-detect AF when focusing to achieve focus. Newly-designed NIKKOR Z lenses take full advantage of this system, providing faster, quieter and with increased AF accuracy than previously possible for both still images and videos.

3. The new EXPEED 6 image-processing engine for sharp and clear imaging, and new functions that support creativity
The Z 7 and Z 6 are equipped with the new EXPEED 6 image-processing engine. Employing the superior resolving power of NIKKOR Z and NIKKOR F mount lenses, subjects are rendered more sharply than ever before. Noise is also effectively reduced.

Additionally, a mid-range sharpening option has been added to Picture Control sharpness parameters. This option, along with existing sharpening and clarity parameters, allows users to make various textures within the screen sharper or softer, for both still images and video3. The cameras also offer 20 options of Creative Picture Control, supporting creative imaging expression. The effect level is adjustable from 0 to 100.

4. An electronic viewfinder that utilizes Nikon’s superior optical and image-processing technologies to offer a clear and natural view
The electronic viewfinder adopted for the Z 7 and Z 6 is comfortable and easy to use, comparable to optical viewfinders. Both cameras are equipped with an electronic viewfinder for which an approximately 3690k-dot OLED panel has been adopted. The electronic viewfinder has frame coverage and magnification of approximately 100% and 0.8×, respectively, as well as an approximately 37.0° diagonal viewing angle. It draws on Nikon’s superior optical technologies and image-processing technologies, ensuring a clear and comfortable view, with reduced aberration and minimum eyestrain, even during extended shoots. Furthermore, a fluorine coat that effectively repels dirt has been applied to the eyepiece protection window. In addition, the menu can be displayed in the electronic viewfinder, allowing users to quickly view and adjust a variety of shooting settings, including ISO sensitivity, AF-area mode, and Picture Control, all while looking through the viewfinder.