It's been a while since I played the PSP version, but I know the Int-Spirit penalty from the original was removed, the game retargets normal attacks when an enemy dies, inventory space is unlimited (?), and general enemy strength has been toned down (or, conversely, player stat growth rate has been ticked up, not really sure which). It's also got a bonus dungeon with new ultimate spells and the Dawn of Souls storyline in it.