I think that a 5D mkIII review and contrasting it with the D800 is well worth the effort. The 5D mkIII has lots of improvements over 5D mkII and in many ways a more general purpose camera than the D800.
I wouldn't say that. They both seem pretty general-purpose to me.
The D800 has the advantage if you need to print large - you can print 27% larger on each dimension while maintaining the same resolution (upsampling is useful, but doesn't give you more actual detail). At 24" print width, you're getting 307ppi with the D800, vs 240ppi with the 5D3 - not all that noticeable. At 36" width, you're getting 205ppi vs 160ppi - starting to be noticeable. At 60" width, you're getting 123ppi vs 96ppi - this is very noticeable.
Both are good in different forms of challenging lighting. In extreme low-light situations, the 5D3 seems to have a slight edge at ISO 25600 and above; they are about equal at ISO 3200-12600 (I couldn't tell the difference on 16x24" prints) and the 5D3 is decidedly inferior below that (similar noise on the pixel level, but the D800 has 70% more pixels). So, if you're regularly shooting at greater than ISO 12800, the 5D3 might be better. But, really, if I were shooting at such high ISOs routinely, I'd be looking at the D4 or 1Dx, rather than either the 5D3 or D800. In situations of high dynamic range, there's no contest - the D800 is simply better.
That the D800 came around at 36MP should not really have been a big surprise since we already saw what such a sensor could bring from the D7000 sensor and other cameras using the same sensor. The next step up for Nikon (and Sony) for full frame would logically be a FF sensor based on the 24MP APS-C sensor giving a 54MP sensor.
To me, this is a huge milestone - 150ppi at 40x60" print size, or 300ppi at 20x30" print size. The issue, of course, is lenses can keep up in the corners (time for a 14-24 Mk II from Nikon, maybe, and
definitely time for a 16-35 Mk III (or a 14-24 Mk I) from Canon). Canon's TS-E 17mm and 24mm are definitely up to the task; I wouldn't mind seeing a TS-E 14, though, for tnose situations where you want to capture all the width in a single frame, but need the tilt function for focal plane control (would be OK even if the shift were limited, as long as there is tilt). Nikon's PC-E lenses probably need a revamp - and, given that Nikon's latest camera is pushing the boundaries of medium format, and many medium-format photographers need their movements, there's every reason for Nikon to be heading in this direction (the recently-patented PC-E 17 may be indicative of this).
What is more surprising is that Canon chose to stay at 22MP and not base a new FF sensor on the 18MP APS-C sensor which would give a 46MP sensor.
Because it's sufficient for event and wedding photographers. But, with no high-resolution replacement for the 5D2 and 1Ds3, it's left studio and landscape photographers deeply disappointed. After all, many people bought into the 5D2, coming from MF film, when it came out for its high resolution - 21MP was huge in 2008, when the standard was 12MP - not for its other features. These same photographers are still shooting the same things - requiring high resolution and dynamic range, not so much high ISO or frame rate - but, for their purposes, the 2012 model is no better than the 2008 model.
Thoughts about these choices and why they were made and where we are heading for the future (and as mentioned what is relevant for real photography of various types) might be more interesting than how much you can lift shadows from the D800
For sure, but definitely not to downplay the DR advantage. The superior shadow detail is a
huge deal. If you've ever taken a landscape with a recent MFDB (single frame, not multiple exposures), exposing for the highlights then recovering detail in the shadows, you know how detailed and noise-free the shadows are. You can do the same with the D800 and D7000. With the 5D2, all you get is mush and pattern noise. There are many situations in photography where you can't take multiple exposures (moving objects), can't use GNDs (uneven horizon) and can't use fill flash (distances too great) but need detail from shadows as well as highlights (usually involving backlit objects during the 'golden hours', or silhouetted against the sky).
Come to think of it, the D3x was announced on December 1, 2008, when the 5D2 had been available for barely a month, and still had the 'black dots' issue. If, instead of releasing a $8000 camera, Nikon had put the same sensor in the D700 and called it the D700x, the 5D2 would have been stillborn - many of those who moved from MF film to the 5D2 would have, instead, moved to the D700x. Similar price band, higher resolution, better DR, better AF, better weather-sealing. Slower frame rate, but no-one ever bought the 5D2 for action shooting anyway.