Nikon say it's not a replacement for the Nikon D700 model, but sit alongside with it.
What's new with the Nikon D800?
Check the sample gallery provided by Nikon
I will not go into details with this one, but the camera video samples show that its a promising camera in this field, and I am sure it will compete head to head with the Canon 5D Mark II.
* Full HD 1080p at 30/25/24p or 720p at 60/50p in AVC format
Nevertheless, Nikon claims that the Nikon D800 has 36 new features/improvements compared to the Nikon D700. Personally I think that the additional MP count and the HD video are the two main improvements that Nikon users were waiting for. Although, I was craving for higher performance at high ISO, performance close to the D3s or D4.
This is something I personally thing it's going to benefit landscape photographers the most, it will make their life much easier. The camera can combine 2 exposures at up to 3EV.
The E version is specifically targeting landscape and studio photographers who aim for that extra bit of sharpness, but as a tradeoff it increased possibility that moiré and false color will appear. And Nikon decide to include a new filter in its CaptureNX application to remove the effect. So, which one is for you, it's your decision.
Nikon D800E Sample Gallery from Nikon
Many will be dazzled by the 36 Megapixel sensor the D800 provide and many others will buy it for the HD video capabilities. It's a great camera and an impressive addition to the Nikon DSLR family.