I am playing 358/2 days, and I find the story itself - as usual - very nice. However, it gets kind of boring that you "only" have to do those missions for days - and they're always the same. I really wanna play only because of the story and because I'm a fan of the series, otherwise I agree with you that it is not that a good game. You only miss the story, which is very interesting and catching as usual.
As I know lovely Kairi she will lend her PSP to me one day, so I can actually play Birth By Sleep too (I actually have her DS at the moment

)