Nikon's new $3,500 D2H is a successor to 2001's D1H, and its obvious competition is still Canon's EOS-1D. Nikon has a new internally-designed sensor, identified by a mouthful of letters: JFET LBCAST (junction field effect transistor lateral buried charge accumulator and sensing transistor array). The sensors are similar to the CMOS sensors used by Canon (relative to CCDs), with some technical differences you can look up elsewhere (like Phil Askey's review). One effect of moving from the CCD used in the D1H is that the D2H has lost the super-fast 1/16,000s electronic shutter introduced back in the D1. (The D2H is "limited" to a 1/8000s mechanical shutter and 1/250s flash sync.)
The switch away from CCD was professedly to reduce noise in the captured image. The most comprehensive comparison of Nikon's noise characteristics is in the Imaging Resource's review which plots noise against the EOS-1D in both daylight and low-light across the range of ISO settings. If you are interested, I suggest reading through the section of the review, but the short of it is that the Nikon performs better in low-light (daylight is a mixed bag with Canon doing better at lower ISO settings).
Compared to the EOS-1D, the D2H has a smaller sensor (higher focal-length multiplier) and can shoot at 8 fps for a full 40 shots, while the EOS-1D gives-up between 2-3 seconds (16 exposures raw, 21 JPEG). The D2H has video out (NTSC or PAL) and USB 2.0 transfers, but has lost IEEE.1394 and support for GPS receivers. It does support the optional WT-1 802.11b wireless transmitter which allows you to transfer captures over WiFi networks while untethered. The camera is quick, it is ready to shoot as soon as you turn it on, has 100% coverage in the viewfinder, and is built solid.