New localization & restored content (US version)
The translation is much closer to the original Japanese version. More importantly, the alternate major plot path (Snow Queen quest) which was cut out of the English PS1 version has been restored, drastically increasing the overall length of the game.
Movies added between scenes
Some songs are remixed whereas many are all-new. The music style of the new songs is much more similar to P3 and P4.
Two new dungeons are added. One for the SEBEC route and one for the Snow Queen route.
Readjusted game balance
Encounter rate and dungeon construction were revised. Players can also choose different levels of difficulty at the beginning of the game.
Loading speed improved
Load time is shortened by about 60% (even shorter in the PSN version). A new option to skip animation in battle further increases the game's speed.
Save points reassigned
More save points are made. Instant save is also possible in the PSP version.
Revamped 2D city map
The city map is much easier to navigate.