Oedipus "accidentally" killed his father and had children with his mother. He brought disaster to the kingdom and took off his eyes when he found out. He is a similar tragic character to Kratos. Oedipus regretted and was haunted by his actions. But you see, Kratos' mistakes had no effect on his character. Because of GoW2 and 3 it appears that the past didnt teach him any lesson. To the contrary he became even more merciless, he acted worse than he did before he killed his family, he was committing hubris against the Gods which usually leads to the fall of the one doing it in Greek mythology (but not in GoW2 and 3).
Ironically what Kratos hated in Ares and what Ares was doing in GoW1, he became the exact same asshole and then decided to multiply it by 100. He was causing pain and misery to everyone, killed families and other people's loved ones, and he was terrorizing and destroying cities just as Ares was doing in Athens in GoW1.
There is no sense of katharsis in the story after the first game, because he went into a mindless killing spree, with no real purpose, no real goal. It was all about revenge because the Gods turned against him, when he was killing and destroying Greece without giving a damn about the rest. He basically wanted revenge because the Gods tried to stop his selfishness.
Its like you are trying to stop your troubled child from harming others even though you had your best intentions, and then that child reveals his inner serial killer personality and kills you, his brothers, his sisters and mother for trying to stop it.
Whatever you do, you cant stop it from being an asshole. Whatever you do he will try to take revenge on you for its own mistakes.
How could he not feel mercy for Hephestus when he shared a similar fate as him (imprisoned by Zeus and taken away from his loved ones), or spare the life of Poseidon's daughter when she was helpless like his family is beyond me.