The only PSU series title that's really worth your time is Portable 2, but that's not out here yet. I can't speak for the story (I would assume the story's just as awful as the rest of PSU's, but I can't read much Japanese, so I won't actually know until the US version comes out), but the gameplay was quite solid. Force is a little difficult though.
Also PSP2's retaining its online play when they localize it, which will be awesome.