I have bee saying this for YEAAARS. First off, MMOs are different then normal games. People who play MMOs don't have to play as a badass. That being said. I believe that it could be a very good MMO if done right. Kratos has a brother in the underworld. Who is planning his revenge on kratos(According to God of war I) They could do something where he is planning a a hostile takeover with souls from the underworld. One side plays as the minions of him(I am assuming the new lord of hades after hades dies in 3 assuming he does.) vs the minions of mount Olympus(Kratos and his ilk. Titans also if he doesn't kill them in 3 lol. And the dead gods souls could be trapped in hades and are still around in spirit form in the underworld.
The enemies you face really would give you a huuge potential for classes. As for one side, they could be the monsters. Cyclops = tank, Minotaur = melee damage The dudes who summon monsters in 2 could be a pet class, archers could be.. well archers.etc etc. On the other side you can have real normal classes as humans, centaurs, Demi gods, etc etc. Humans could be Paladins(or a greek version) also archers and the summoning class. Centaurs could be archers, melee damage, ad a holy healing class. Demi gods could be tank, Melee damage, and ranged damage.
All the workings are there.
Oh i forgot, the combat could be a hybrid of the controls now, and the controls of FFXI.
You still fight normally like you do. But when you hold down L2 you bring up a macro menu same for R2. Not sure how it would work if the evasion was in there. Cause that would obviosuly give skill too much weight.