Actually, it appears that the gradient is only at the beginning of the departing runway and vice versa for the arrivals. This would presumably give a reduced accelerate-stop distance since the bulk of the speed is gathered on the downhill, while the stopping is on the flat.
I can see problems with this (a runway overrun on arrival would involve a slide right through the terminal...) and the go-arounds might be tricky with departing traffic directly ahead. They're not insurmountable, though.