If you understand Japanese, a casual gamer or a Symphonia fanboy/fangirl, this will be one of the best buys.
For starts, the graphics take a cut on the PS2 version, partly because the cel-Shaded graphics don't show out so well, and the graphics processor isn't powerful enough. Loading times are also longer on the PS2, due to the disc size being larger. At least you don't need to switch discs anymore.
Apart from that, this game is still worth while if you haven't gotten the GameCube version. Nothing much has changed in storyline or gameplay, but most characters have additional skills and combo attacks and a new costume makeover, provided you bother to get it. The PS2 version is also more balanced out, making sure that Lloyd isn't your main powerhouse all the time. For exaple, Regal now has unison attacks [in the NGC version, he didn't have any at all.]. The best of all are the new hi-ougis. Most characters now have 2 Hi-ougis at their disposal. However, Lloyd, Collet or Genius gains no new hi-ougis and Regal and Kratos only has one. This version also seems a bit mroe bias to Zelos, allowing him to have two hi-ougis while Kratos only as one. Extra side-quests will also allow you to kill off time that you may have at your disposal, allowing you to udnerstand each character more. However, everything's in Japanese, which means you may not be knowing what they are talking about.
Tales Of Symphonia is a great port of the original, with added stuff and a more balanced gameplay. It's a pity that an English version will never arrive; this would have been a best seller