What are some good PSP games that you would recommend?

I've gotten back into PPSSPP emulation, so I'm looking for some games to play on it. I'm more than happy to try out games that are diamonds in the rough, and other lesser known titles. Lay it on me.

i know people probably disagree, but i had a LOT of fun with Rengoku as a kid. it's really repetitive, but the boss fights i remember being very fun. dunno if i ever finished it tho