Get Chains of Olympus.
I just got this game, and it's incredible. Far and away the best game on PSP. It has a few limitations, such as the one analog "stick" and no L2/R2 buttons, but it does well with what it has. Ready at Dawn have become really good. Really good.
They've made no overwhelming changes to the formula, but it's a PSP game, and PSP games don't generally do that. Besides, why would you want to change the God of War formula?
It's not quite as amazing as the PS2 games or the soon-to-be-PS3 game, but like I said, for the PSP's architecture, and the limited controls, it does very well for itself. Oh, and it doesn't star Kratos' sidekick, because he doesn't have one (Daxter, Secret Agent Clank, come on!)
The graphics aren't a scratch on God of War II, but they are almost as good as the original, again, surprising considering the PSP's limited power.
My overall score so far: 9.2/10.
*Prays for 2009 release of God of War III*
(Former) Lead Moderator and (Eternal) VGC Detective 
