It's a shame GPU Physx only works with Nvidia hardware, I would rather see something like TressFX (DirectCompute or OpenCL) which works with any GPU (Intel, NV, AMD), even if performance is a little lower... but I guess it makes more sense to NV to claim this kind of advantage, but since the game is multiplatform I doubt the advantage of NVGPU Physx will be to significant.
as for Witcher, I enjoyed the first and second game, but I still think apart from visuals the first was a better game, bigger, more diverse, more interesting.. let's see what they can do with Witcher 3, it's a much bigger world, let's just hope it doesn't feel to empty.