OK,
When shooting ISO 64 or 100 - for landscapes or high contrast scenes, the D810 is the king of all DSLR. I give it to them. The DR is truly massive and impressive. Shadow lifting is exceptionally super clean compared to the competition.
However, the tones suck and are flat. For such scenes, when possible (which is most of the time), I achieve much superior results using HDR. Nothing beats feeding the sensor the light it needs to give those great tones, colors and sharpness. The premise here is that I reject the notion of even having to do all this shadow lifting.
The 5DS with its higher resolution, sharper Canon glass, better color and HDR technique produce superior results. The D810 is the winner for capturing high contrast scenes with moving subjects where HDR is not possible. There, shadow and highlight recovery makes for a better image, even if those areas are flatter than one would hope for. It's a forced compromise. For static shots, that flatness just isn't optimal. There's greater image potential and the high DR shadow lifts and highlight recovery of the D810 doesn't cut it. It's ok for common folk who don't know the difference, but for those who scrutinize image quality - not appealing.
DPReview goes a little too far with the whole Nikon under exposure metering. To say that to go ahead and underexpose everything to preserve highlights, and lift all the darkness in post. That the metering system enables this kind of practice.
Uhhgg...
First of all, this might be fine for some tech geek who shoots a handful of shots here and there. But that to me is not professional in the slightest. Having to exposure correct hundreds of photos (perhaps thousands if a wedding) in post is NOT my idea of good process. That is a serious time killer, and time is money. It would have some merit IF the results were great and could lead to a return. But they don't. It is more efficient and the results are superior to have quality lighting. I've seen these bozo wedding "pros" show up at events with their Nikons, fast primes ready to do their "natural light photography" ...every time, at least to my eyes and tastes, the results look like vomit. The best work I've seen is done by those with quality portable lighting systems. It is so cliche. It's the same formula, Nikon + fast primes and no lighting - ready for "natural light" photojournalistic wedding style. AKA, crapola. My advice to couples is to not hire Nikon shooters who don't bring lighting gear and carry lots of primes.
Going +2 to +3 on most photos? Terrible practice and workflow. I spend enough time, with an already better color reproducing Canon system, doing advanced, yet subtle, color corrections in post - that to add in all these crazy exposure adjustments, shadow boosts and other nonsense. Because to help make these flat shadow and highlight areas come back to life a little bit more, requires even more work in post to enhance the color, saturation and contrast in the most realistic way possible and to do so selectively in those regions. Too much work, too much time. All in an futile effort.
Like I said, no problem for the hobbyist. He has all week or more to sit down in post to tweak a few images. Those trying to make money at this are not having that. Just not possible.
To make a great photo, regardless of sensor - you must have a good exposure. No getting around that. Sure, the newer technologies do offer up more latitude. But that doesn't mean you have to use ALL of it. Just because it can bring 5 stops into the correct exposure doesn't mean you have to. What it means to me is, if it can cleanly move over 3-5 stops, then a reasonable adjustment of 0.5 to 1 stop will be that much better than previous generation sensors. Does that make sense? They're so good now, that you don't pay any noticeable penalty for a reasonable exposure correction or shadow/highlight recovery. 3-5 stops has a penalty, even at ISO 64 with the almighty Exmor with nearly 14 stops of DR. The strength of that sensor is you can do small adjustments with zero detectable penalty. Key word, small. Not work the sliders to create bizarre looking images with flat areas void of quality tonality.
All of the DR advantage is gone by ISO 800. ISO 800 these days is NOT a high ISO by far. For events, there's no DR advantage, but you do take a noise penalty vs. other cameras. This to me, means the D810 is not the all-around camera some claim it to be. Also, at least for me, low-light AF accuracy and speed is critical. I've shot in low light situations where I had to put down the 5D3 and go to the 6D to lock focus faster. D810 not cutting it at all in this area. Making it useless for entire segments of semi-pro DSLR users. There's also the gigantic file sizes.
It doesn't make sense to me...the D810 is a great landscape machine, but when you're doing landscape - you're already committed to a lot of post processing, why bother with all the exposure tweaking and just move to HDR and get better results? At which point, I'd rather have Canon color and tones, and the better Canon glass selection. I've created noise-free images using HDR techniques that have amazing IQ. There's no Exmor, high DR shadow lift in the universe that can yield better results.
For events, it is not a good camera. Especially with the lack of custom modes. Canon's C1,2,3 modes are almost priceless. Being able to make a 1 click adjustment and have the entire camera state, all settings change is extremely useful. Especially for events. Nothing is faster for transitioning the camera to take optimal pictures for changes in scenario, whether it be outdoor vs. indoor, or stills vs action. Good luck fiddling with all the dials on the Nikon to pull off the best results in diverse event. Not happening. Instead, you'll end up with some marginal shots that will need a lot of POST processing.
Hence, the "go to black and white" crutch. AKA, the shot is needed, but was botched - so make it B&W. Client might consider it artistic license and style. Problem solved LOL.
Nikon glass also has some heinous lateral fringing of the purple kind. Not all their glass but a lot of key glass does. The kind of key glass one uses for headshots or portraits where enlarged prints could be scrutinized. The 85mm comes to mind. Sure, there are corrections for this. But why have to? Corrections come at an IQ penalty. Canon isn't perfect, but they ensure that the needs of real pros are met. Pros often value things quite differently than tech-geeks.
I'm not a pro, but I've shot some events and worked with many pros. Some who are great, others who are charlatans.
More DR is always welcome, but there's just too many pros on the Canon side that outweigh it. The D810 is a good camera. It's just not an all around camera, nor is it a serious pro camera. It's a great hobbyist camera.