These are hardly original thoughts at this point, but I thought I'd add my observations of the D810. I'm coming from a background of using the D800E and D4 for the last few years, and I've used most of Nikon's FX cameras since they were introduced. I've also used Canon’s, Fuji’s and others.
- This is the best general purpose camera I've ever used. I don't say that lightly, but Nikon has refined this camera in so many ways that are photographer-centric - it's impressive. I find myself repeatedly thinking "This is perfect. It's exactly how I would have updated the D800E" or "This is exactly what I want in my primary camera".
- The shutter sound is about half as loud as the D800E: it's a nice, muted "thunk". Perfect. It's about half way between the regular, very tinny sound you get from a Canon 5D Mark III and the 5D's quiet mode, which sounds appreciably better than the regular mode. While the latter is very nice, you lose frames per second, which you don't with the D810. This benefit is partially psychological (it's much more of a pleasure to shoot with it), but it's also a real factor in some shutting environments. The D810 is less likely to be noticed in quiet environments.
- Live View is greatly improved. If you zoom into the equivalent settings on both the D810 and D800E (100% equivalent), the D810 is far sharper and clearer. No comparison.
- Electronic first shutter curtain is a great change that will make it easier to get sharp results on a tripod.
- Autofocus appears to be quicker and more sure-footed. I see less "dithering" when I use lenses like the 80-400mm AF-S at 400mm. It's a bit too soon to declare victory on this, but so far so good. Every shot I've taken so far is consistently sharp. The new group AF feature will be very good for shots where the principal subject fills up a lot of the frame.
- Image quality is great, just like the D800E. I haven't bothered to make comparison photos and probably never will. Both cameras are great in this respect.
- The increased frame rate (five fps vs. the four of the D800E), combined with the revised autofocus, makes the camera feel more responsive. That extra frame per second matters with some subjects, so it's a welcome change.
- The highlight-priority matrix metering feature works exactly like you'd hope, at least so far. Shots that are overexposed on the normal matrix metering mode have perfectly exposed highlights when set to this mode. I'll use this metering mode a lot with landscape shots.
- This camera feels much nicer in the hand than the others in the D800 family. The revised grip fits my hands perfectly. I always felt like the Canon 5D MIII felt nicer to hold. The D810 is just as good as the Canon in this respect, and that's high praise.
- Auto bracketing now works in increments up to three stops! This is great for shooting handheld HDR sequences!
- The construction quality is just as nice as the D800E - very solid.
- Having ISO 64 as a native ISO is great. That extra 2/3 stop of difference reduces the number of occasions I have to use an ND filter to get a slower shutter speed.
- I'm using the release candidate of Adobe ACR 8.6 with my own color profiles. I'm not seeing any of the publicized problems, but I'm not trying hard to do so. In "normal" shooting, raw conversions from it look great. That's good because NX-D is very cumbersome and slow.
- The video improvements are nice updates, but I don't shoot a lot of video. I'm certainly not going to complain about the improved quality, zebras, etc.
- I'm glad Nikon didn't change the overall shape of the camera too much. My RRS L-bracket that I had on my D800E fits just fine on the D810. As before, it's not easy opening the rubber side panels with the bracket in place - a paper clip or fingernail file on a Swiss Army knife helps.
Conclusion: It would be easy to dismiss the D810 as just a warmed over D800E, but in my experience so far, that's just not the case. This is a very refined camera that just works. As nice as the D800E is, it'll definitely go to a backup camera status. For me, enjoying photography isn't just about the final result, it's also about the pleasure of using the camera and lenses. I like equipment that works well, offers a good shooting experience and "feels right" in the hand. The D810 is as good as it gets. Nikon gets an "A+" from me on this camera.