I just picked this up yesterday, and its damn excellent. The graphics are top-notch for PS2, and it has a metric shit-ton of characters. Every one who was ever in any Soul game is there, plus a ton of new and "bonus" characters, including the ORLY owl. I think I counted 41 selectable characters in total, plus you can have 10 custom characters per memory card.
The "Tales of the Soul" story mode gives you a complete story for every main character, including branching baths and QTE-action story events, plus lots of cutscenes with dialogue.
Then there's the "conquest of the sword" mode (I think that's what it is called), which is like a strategy game mixed with SC type battles. You build your army with story and player-created characters, set their class/unit type/weapons/armor and then battle to take over bases and fight various bosses and challenges. It's a lot like Ogre Battle, but instead of RPG fights you do SC missions.
Then there is the regular arcade type fighting mode, where you just fight 7 random opponents in a row, and the boss, and try to get the best time/score. But there is also a tournament mode that has elimination and round-robin type tournaments.
SC always has a lot of unlockables, and SC3 doesn't disappoint. You earn gold for pretty much everything you do in every mode of the game, and you can spend that at the Weapon, Armor, and Item stores. The item store is where you get all the bonus stuff like art galleries, weapon demos, more modes, more playable character classes (ninja AND pirates!) etc.
The character creation is pretty fun, you get a lot of parts and job options, but you can't adjust your characters proportions! SC is famous for its amply busomed characters, but you are stuck with one size-fits-all homebrew characters. Crushinator am cry. I got the right parts to make FFXI AF THF Crushinator though

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If you liked any previous SC's 3 will not disappoint.