I once did some basic rigid body physics with it and it was quite easy to realize, not as easy as with newton, I am pretty sure that there isn´t anything easier, but at least it also wasn´t much harder. It was also quite stable and very fast. Bullet in comparison is also very nice, but a LOT harder to use...

With basic rigid body physics there may not be that much difference but when it comes to stuff like contact manipulation and custom joints and so on then it starts to get interesting. PhysX is surprisingly limited in this regard.