The low light performance was my main reason for buying. I can shoot ISO 6400 and still produce useable and great images. ISO 3200 is what I use most and it's fantastic.
The LCD screen is awesome. Much better than any other DSLR screen I have seen. And still much better than the ones on the 1dsmk3 and 1dmk3.
The FF sensor is great. Nikon got it right on their first turn.
Dual CF card slots are only found on this camera and Nikon are geniuses for incorporating it. For wedding photographers and professionals, losing images due to an accidental delete or card failure is the worst possible senario. Being able to RAID 2 CF cards prevents the problem of card failure occurring. I currently have 2x 16gb cards in my D3 which provides me more room than I need. When shooting for myself, I can make SLOT 1 overflow into SLOT 2, which gives me a total of 32gb of storage in the camera.
People may complain about the cost of this camera, but as a flagship camera for Nikon, I don't see what there is to complain about! It is the best camera on the market in my opinion and worth every cent. For the price, you get a hell of a lot.
If you are considering this camera but the price is making you weary, GO FOR IT! Trust me, it is worth every cent and you won't regret it.
Paired with the Nikon 24-70mm 2.8 and the 70-200mm 2.8 you have the best combination kit possible.