the answer requires a lot of stratagy. i mean more than the main game because the enemies are just so hard and can easily kill you. it was ok but too frustrating to really be replayable
persona 3 portable has minor changes to gameplay like letting you control everyone's actions.
you get boss rematches against the full moon bosses and you can fight Elizabeth's sister
the main appeal is that you can play as a girl and social link's are different if you do
you get junpei, akihiko, ken, shinji, and koro. you can have any of them as a lover, except junpei i think, and you can save shinji
oh and you can't have koro as a lover either because human and a dog...O_o
i think that alone is worth it, just to see the new social links
on the other hand, we no longer have anime-style cutscenes which has to take getting used to.
so in short, i love person 3. it's the only persona game i ever played though