Anandtech is running a story about the hardware of the new Xbox 360.  They took it completely apart and looked at its guts.  The rundown is: it consumes less power, makes less noise, and has much better cooling hardware. 

One question has been answered (sorta): There will be no more RRoDs with the new one.  I say that because there are no red indicator lights on the front; the green lights flash when there's a problem.

If you really want to see the guts, see the story at Anandtech.