Another area where Nikon kind of copied Sony -- and was smart to do so -- is in video. Much like the A7 III compared to the A7R III, the Z6 actually has better video capability than its more expensive Z7 sibling. That's because the Z6 can do a full readout of the sensor and supersample it, resulting in exceptionally sharp 4K video. The Z7, on the other hand, does some line-skipping at full frame, so you need to crop to APS-C to get the sharpest possible video -- exactly like the A7R III.
With the Z6, you not only get sharper video but can benefit from the full-frame sensor's excellent low-light capability and shallow depth of field. That makes it more practical as a documentary or cinema camera as you won't need tons of lights to shoot at night nor fast lenses to make your subjects stand out against their backgrounds.
It actually bests the A7 III in a key area: offering 10-bit, 4:2:2 log video output to an external recorder. That gives you more dynamic range (and colors) to work with in post-production, especially if you're shooting in tricky lighting. It can also handle slow-motion at up to 1080p 120 fps, but unlike the A7 III, it has to crop down to APS-C to do that. Finally, the Z6 (and Z7) offer separate exposure settings for video and photos and let you define custom i-menus for each. That's key because video and photography are two completely different disciplines and separate settings make it easier for folks (like me) who switch back and forth.
Despite the autofocus system's fussiness when tracking subjects for photos, the Z6 has excellent AF video capability. It's not quite as good as Canon's Dual Pixel system, but I think it's just as good as Sony's offer on the A7 III. And unlike the Canon EOS R, the Z6 has in-body stabilization, making hand-held shooting a bit easier, especially for non-professional users. It also makes it easier to use with non-stabilized Nikon lenses and even the manual non-electronic models popular with cinematographers.
On the downside, the rear touch display on the Z6 can only be tilted up or down and not rotated around. That makes it impractical for vloggers or one-man-band video operations, unfortunately. Canon's rival EOS R does have a fully articulating screen as do Panasonic's popular GH5/GH5s models.
Another issue is manual focus. The Z6 has a focus-by-wire system, so moving the focus ring a set distance won't consistently change the subject focus. That makes it impossible to set lens marks based on where your actors are standing, for instance, and pull focus to follow them. (Nikon lenses also focus backwards from other systems, but that's another story.)
Luckily, most cinema lenses are manual focus only, so the focus-by-wire problem doesn't apply there. And Nikon does at least offer focus peaking when you switch to manual mode, so you can quickly see which parts of a shot are sharp. Bear in mind that you can't use it at the same time as highlight peaking, however, for some reason. This bug or oversight seems like it could be fixed in firmware, so I hope Nikon does that.
While the Nikon Z6 does have both microphone and headphone ports for pro shooters, there is one issue. The pre-amp isn't particularly good, so if you have a microphone with a weak output level (read: something cheap you'd find on Amazon), you'll have to boost the camera's signal, which adds a lot of noise.
Most importantly, I was very happy with the video I shot with Nikon Z6. With full-frame super-sampling, it's incredibly sharp, and Nikon's color science makes it a great people-shooting camera for interviews, short films, etc. Thanks to the big sensor, it also delivers usable images at ISOs up to 25,600, giving shooters the option to use natural lighting, even in dark conditions. Nikon just has to fix a few things (mainly the audio and touchscreen), and they'll have a near-perfect mirrorless camera for video.
With the Z6, Nikon set out to beat Sony at its own mirrorless game. While it didn't quite succeed at that, it's still an impressive debut. The A7 III does have better autofocus performance and also edges the Z6 in image quality, especially in low-light situations. For the foreseeable future, Sony has a much better selection of native lenses, too.
However, the Z6 is actually a better handling camera. And it edges the A7 III in video, offering comparable features, autofocus and video quality, but adding 10-bit 4:2:2 video via the external HDMI output. And while both cameras have in-body stabilization, Nikon's camera might have a slight edge there, too, thanks to the larger mount.
Nikon's lens selection is limited so far, but the potential of the Z-Mount is huge. One of the next models will be the Noct-Z model with a stellar f/0.95 aperture, and Nikon will have 13 lenses in total by 2020.
The A7 III and Canon EOS R are the Z6's biggest competition for mirrorless full-frame cameras, at least for now. Panasonic will soon be releasing its own full-frame mirrorless cameras. Adopting roughly the same strategy as Nikon and Sony, it will launch 24- and 47-megapixel models, the S1 and S1R, respectively. If the GH5 and GH5s are anything to go by, they should be great for both video and photography, so if you're not in a hurry, it might be worth waiting.
If you're willing to shoot with a smaller sensor, consider Fujifilm's excellent $1,500 X-T3, which is the world's best APS-C mirrorless camera, I believe, especially for video. Another great option for videographers is the Panasonic GH5, which handles audio better than the Z6 and has more options (like 4K 60p) for video.
If you want a decently-priced full-frame mirrorless camera, however, the Nikon Z6 is a great choice. It's a no-brainer if you already own (and like) Nikon lenses, especially if you shoot both video and photos. Overall, it's a great start for Nikon in the full-frame mirrorless game and will force all the other players -- especially Sony -- to step things up.