Have only played MGS4. But understanding the popular conception that MGS is unnecssarily complicated, I think that GoW creates a really sympathetic, flawed, engrossing character with a simple, but enjoyable story.

His entire physical body represnts what a monster he become. He cannot ever be disarmed. He literally has weapons as a part of his body, due to the the pact he made with Ares. Even if he wants to stop fighting, his weapons, his chains, will bind him forever. And that inability to stop fighting is what killed his wife and child, and his sins forever stay with him, the ashes of his wife and child covering him, and making him the Ghost of  Sparta.

Unable to be salvaged, unable to take back his past actions, betrayed by fate, entrusting everything into the mighty gods to relieve his pain, and ultimately being betrayed by even the rest of Olympus at the end of God of War, frusturated by their powerlessness, and his own, he can never turn back, after killing Ares, he truly become the God of War.

After his tragic fall, Kratos essentially self destructs. He's now on a simple rampage, as he now lost all hope to shed his pain, his memories, and his fate to an eternity of fighting. Hopefully in the final game we can see some conclusion and salvation, or it can end like it did in the first God of War, again, Kratos destroying everything, and remaining as an being dedicated to war (hopefully there'll be player choice, and we can either make Kratos stop his rampage and let go of his past and guilt, or continue his destiny of being the God of War.

Edit: It's 3:00 AM so give me a break on my shitty ass typing and inability to really piece together my mind and thoughts. I'm dead tired, Kratos is awesome, Sam Fisher>Solid Snake, good night.