FFT: War of the Lions should give you about 60 hours of gameplay.
FFVII: Crisis Core won't be your thing unless you have played/replay FFVII
Disidia: FF is a fighting game, real diverse and complex gameplay, plenty of equipment and so much unlockables. but you'll probably only love it if you like FF and even if its still alot of the same things over again. (I skipped most of the cut scenes cause they were corny and dumb.)
PSP game selections is horribly bad right now, the DS absolutely tramples the PSP sellection... but i havn't bought a DS yet.
