You just mentioned blocking the sides and front of your face. That's WAY more realistic because obviously in real life, attacks can come from all directions. The directional blocking system I've mentioned numerous times would be perfect. To give you an understanding of what it's like, think of FNR 3's parrying mechanic. Where you hold a button to initiate the guard, and then flick the right stick in the direction of the strike to successfully parry. This is similar except you replace the parrying with blocking of course! Now, you will actually have to react to individual strikes so if someone's throwing a hook, uppercut, or straights they will actually matter.