..... over on DPR
My quick take is that it looks to be almost identical to the D3s, obviously with slightly more detail in them due to the slightly higher pixel count.
Both Nikons look clearly better than both Canon comparisons(5D MkII and 1DsMk4), but time will tell how the 5DIII fares against them.
In some ways the D4 sample looks better than the D3s, and in a few other ways the D3s looks better at higher ISOs .. mainly in the 12800 and above images.
Colours are way better from both Nikons than from the Canons, and in general the colours from the D4 look better than the D3s, but on the Kodak colour chart in the upper right in their studio scene, the colours from the D3s look better(less washed out).
Anyhow .. now, if I were to choose between a D3s and a D4, it'd be the D4 only for the video functionality.
Updating simply for better noise quality in low light doesn't appear to be worth the effort(yet).
Of course this depends entirely on DPRs D4 images and whether they're using a production (firmware) camera, or just from the pre production camera they've had for a while now.