The story line is amazing. Every new mission is another twist and turn. I beat Metal Gear RAXA a few weeks ago and I thought it was the end too since that psychic was in it. But when Gene started laughing I think I yelled "Damn" ( ask dancy_SAZ if I did or not I don't remember). At the moment I'm about to break into the missile silo to find the nukes.
I've played most of the must have games for PSP. Right now I'm playing Valkyrie Profile: Lenneth again for ending A since endings B and C weren't the real endings. Another must have for PSP is Lumines. I prefer the first one over the second but its certainly a must have.