It would be interesting to have special unlockable stuff after finishing GOW single player. You wouldn't have to use these unlockables they would just be there for some added bonus'
Some of the stuff that you could unlock could be:
.All locusts wear pink aprons
.Marcus wears pirate hat (arrgh)
.Different Phrases from COGs
Post some of your own ideas of some stuff to unlock.
These are just some ideas if there are any unlockables at all.