The blurring effect occurs in two situations.
When you have the Motion Effects turned on and you move the details will blur.
Even when this is turned off, you will experience a blurring effect when dealing sustained damage to enemies, especially when chaining combos together. The more combos you use, the longer the effect will last. It is supposed to represent your rage - the higher the rage, the longer the effect.
I've found it a little disorientating too. It's only after you've reached Fury Level 26, your vision clears, and you notice that ALL your enemies' torn body parts are scattered across half the level that you appreciate what the higher Fury Levels can do
