I rather liked Daxter and Dissidia. The God of War games for the PSP weren't terrible, but not great. They're fun for what they're worth. Ghost 'N Ghouls is about the closest thing to a decent 2D platformer I can think of for the system, outside of homebrew. LittleBigPlanet is an ok game to mindlessly pick up once in a while and waste a few hours on. Wipeout Pule is like a fusion between F-Zero and Mario Kart, so it's rather fun.
That's all I can really think of off the top of my head I'd recommend for OFW. I've heard some interesting things about the Persona series and will probably check out Persona 3 Portable, but I'm not much of a JRPG person outside of Final Fantasy VI and IX.
Homebrew game wise, I have to recommend Cave Story (easily my most favorite game on the system and a good port) and TetriAbetes (or some other Tetris knockoff, can never go wrong with Tetris).