Cool, yes, but cool is not the same as good character development. Killing defenseless people in needlessly brutal ways, much like using babies as human shields or raping the girl who has a crush on you, are all things you have a character do when you DON'T want them to sympathize with a character. They're used effectively in writing when, for instance, you accidentally let your main villain get a bunch of fangirls by playing up his silky european accent and devilish good looks a bit too much, so before you finally kill the guy you show him sodomizing a kitten to cut down his fanbase and remind the rest of the viewers why he's supposed to be dying.
Yes, if God of War were some sort of pretentious philosophical game you could claim they did it to make an artistic point by forcing the player to perform villainous acts, but its not one of those games. So we're left with the author being utterly clueless about effective characterization as our only explanation.