(Since I loathe the US versions, I'll be using the JP terms in my review. If you can't follow, then tough. : P)
Persona 3 Portable is the second remake (and first PSP incarnation) of one of the most celebrated PS2 RPGs of all time. Instead of an epilogue, the plot is revised a little to allow for the choice of playing as a female protagonist. The new girl has experiences unique to her path, and many of the Commu links were changed to match. Some elements from Persona 4 were also incorporated, making the gameplay experience markedly different from the first two P3s.
