I personally like the nudge ability, although I do not think it should affect someone who has their shield up (I never tried to use it against a shielder personally)
It just seems a bit odd that a punch to a raised shield would knock someone off balance while a strike with a weapon does not. Raise the Cooldown a bit and nerf the ability to stun shielders with a raised shield.
Also, for those who believe that 1/2h's should also get a nudge. No.
You guys are already powerful enough considering your attack do as much as great swords with the speed of most 1h weapons, plus your attacks are longer so your are not face hugging like some 1h have to. You already have a bonus for using 1/2h'ed weapons, and that ability to to use it in two hands and use it with a shield if need be.