After a long break from GoW:CoO, I resumed playing. Man, is the Persephone battle annoying; it's not the battle itself, but that you have to wait a few seconds for loading, run a few seconds, and then sit through a cutscene, and then you can try again. I lose focus every time it happens, and it ruins the experience. Why designers keep accepting these things in a modern game is beyond me.
A nice surprise: a checkpoint in the boss fight. Now I'll never have to endure that annoying cutscene again!
completed the game on Spartan (hard) difficulty.
... And she's defeated! Awesome game.