You can always tell what's considered a good game that when you play it so much, you decide to go look for the rest of the series.
Most RPGs these days last about one play-through and then it spends the rest of its days collecting dust. This isn't the case with Tales of Symphonia. In fact, it's the exact opposite. Due to the Grade points that are earned throughout the game, you can make the play-through quicker so that you can try to find every item and explore more or make it harder by reducing the amount of experience you earn.
If you have three other friends, there's always the option of allowing them to play too.
Story-wise, it pales in comparison to most Square franchises but its enough to keep you interested and occasionally, there are a few twists.
The characters are pretty standard: the young hero, the damsel (who faints about every cut-scene), the loner, the lover, the even younger sidekick/friend, the ninja, etc. Although the voice acting is quite professional, the dialogue can be a little cheesy. Luckily, with professional actors, they know how to work with that type of material and it can be overlooked.
Tales of Symphonia has proven to be a wonderful addition to the Gamecube's tiny RPG library. I absolutely recommend this game to anyone, especially now that you can pick it up for less than $20 at most places.