Features an extra disc of bsides, rarities and demos. I usually see this for about twice as much. Blah are even selling the vanilla version of Downward Spiral for £9.19!
As usual, it's remastered (what were they doing the first time around?). Plus it's a hybrid SACD, so it'll play on super audio cd players in super audio quality, I'm assuming.
edit: Forgot to add quidco. Don't you forget it either! ;)