Kratos is not a boring character. He's brutal and violent to cover his past.
He tried to make amends for his past. Killing his family in a raid of a village, but the gods wanted to use him. So he's now out for revenge.
His skin is bound to the ashes of his dead wife and child. Kratos is a tormented character and deserves the right to be angry in everything you see him in.
If you played Chains of Olympus you would have seen that he loved his family. There is a very tough decision at the end of the game that had to be hard for him.