Well, blocking was, for the starters, done much better than in Oblivion. But I think there should have been a way to be able to time and block power attacks as well, the fact that they break through blocking every single time makes blocking kinda useless, especially for enemies.
Some things I'd love to see are the ability to dodge a hit rather than block it. And I'm not talking about the lame dodging you can currently do because enemies are just slow and mindless, I'm talking about enemy trying to slash you from above and you hitting a button that could make your character hop to side and counter. I'd also love to see Assassin's Creed style counter attacks which were, in my opinion, amazing, including being able to counter bare handed and steal your enemy's weapon.
I'd also love to see weapons act the way they do when you hit a blocking enemy with normal attack, instead of it looking as if we're swinging through air and not slashing armored man. And I'd also love to some grapling, but I suppose that could just go under counter attacks.