Not to start any argument, just an experience going from the 5D2 to a D800:
* Auto-ISO - a lot of customisation options: lower-higher high ISO limits, shutter speed limits, shutter speed limits finetuning in relation to focal length (slower,medium,higher)
* Much better AF (in comparison to 5D2)
* Recently needed to use timer release - again, plenty of options to choose from: the delay up to 20s, how many shots are taken at which intervals
* What I miss from the Canon side - the 85mm 1.2 II - what an amazing lens! And generally speaking lenses - the Nikon's seem to have more distortion. It can be easily corrected in post by using lens profiles but this means some image info is thrown away at the edges. Canon LCD implementation for shooting is also better as no mirror moves when pressing the shutter and the Canon's seems to have more clarity meaning easier manual focusing through LCD, especially when darker. By the way, 36MP is not at all that demanding, good results can be achieved easily when handheld and at moderately slow shutter speeds and with less brilliant glass.
* Updated: obviously, the low ISO DR is very impressive.
In order not to do only the talking, a recent shot: