I would say that the Kinesis is in a class above any Microsoft keyboard in terms of ergonomics.
Not only are the hands slanted, but there is more separation between the hands.
It has low-force mechanical Cherry MX Brown key switches that are relatively smooth, where as the Microsoft keyboard's keys bind horribly on off-centre key presses. (Cherry MX key switches are all the rage among PC gamers right now... ;) )
The lack of numeric keypad is actually ergonomically better in that it allows you to keep your mouse closer to your centre.
The keyboard layout can be fully remapped (without drivers, stored in the keyboard) and it can record macros.
Drawbacks is that 1) you must touch-type properly using all fingers and that 2) the keyboard is quite high because of its curved key wells.
#1 isn't really a drawback in the long term though, as learning proper touch typing will make you a better typist overall. It is easier to learn touch-typing on a Kinesis than on a flat keyboard.