The tales series has always been great for action in RPG combat, but lacks the quality of plot for a good game.
In the past, the Tales series has always had fairly standard out of battle gameplay, with the basic JRPG-style of play. It is in its combat that the Tales series always triumphed, with an action-based combat system. The system provided a nice change to the boring monotony of what I like to call the Final Fantasy syndrome. Now, while Symphonia continues to have a fun and fast-paced action system, its on the easy side and can frequently be won by button mashing until its potion (or should I say "gel") time.
Its Symphonia's plot that is the true failure. Now, I understand that the game is meant for a younger audience, but the fact that, when I played through it, I predicted every single plot point sort of says something about the writing and directing. Instead of ragging on ToS's plot progression, I'm going to give JRPGs a little lesson. When you say, collect/destroy/save object X, Y or Z at the temple/dungeon/tower or (insert elemental substitutes here) I get immediately bored because its been done a thousand f*cking times. When you are creating a lifeforce for the universe, think of a new concept, because the first Tales game and FFVII explored that as far as its going to really go. Oh, and everyone has done the whole "the evil guy is actually your father" to death since Star Wars, so you can stop doing that too.
I honestly don't know what it is about this game that makes it so addictive. Its like that smack addiction that is Harry Potter. Really poorly written, really poorly executed and very uncreative, but for some reason you want to keep turning the pages.