Tales of Symphonia isn't Final Fantasy. That being said, it doesn't have to be to provide simply the best RPG experience the GameCube has to offer.
The storyline in Tales of Symphonia is about as basic as an RPG can get. The land of Sylvarant is running low on mana, the essence of life, and it's up to Collete, the Chosen of Mana who was arbitrarily chosen by being born with a stone in her hands, to save the world and restore Mana. Granted, there are a few plot twists along the way that make the journey turn out to be less simple than this simple synopsis sounds, but none of them are all that original either.
The enjoyable part of the game is the battle system, which is known in the Tales series as the "Linear Motion Battle System". Through this, the battles take place sort of kind of like an action RPG, only with the caveat that you only move left and right. This is more of a carryover from the 2D days of the previous Tales games, however, as you really only move in two dimensions relative to the enemy that you are fighting. You can change the enemy that you are targeting, and you will then move left and right comparative to them. This sounds rather awkward, but it only takes a few battles for targeting enemies for the quickest end to a battle to become second nature.
The travel in the game is pretty much standard RPG fare, with travel around the world map done on foot for the most part. Two things make it slightly different: The fact that the battles on the overworld map are represented by either puddles, or little gerbil-looking things, that are moving around the map. Running into one of these instigates a transition, then a battle. There are no truly random battles, and most enemies both on the overworld and in dungeons are avoidable. Enough enemies are fast enough to get you that you won't be running through the game without fighting, but if you don't fight, you could find yourself completely stuck.
The other little wrinkle in the overworld map is the addition of various little events that you can find scattered around the map, including conversations between characters, chests, and "guideposts" that allow you to move around the map faster, at the cost of not being able to see the previous two events.
The dungeons, and the puzzles that go with them, are pretty standard fare: there's the dungeon full of traps that do damage to your party out of battle, the fire dungeon, water dungeon, ice dungeon, and so on and so forth.... again, mostly standard fare. It's like they took all the dungeon types from Legend of Zelda: Ocarina of Time and made them for this game. It's all executed really well though, so as you go through the puzzles, between the easy ones to the moderately hard ones, you don't really mind that you've done this all in other games.
Another unique feature of the game is the "skits" that are frequently triggered in the game simply by walking into certain areas or talking to certain people. They're triggered by pressing the Z button, and they involve portraits of the characters with subtitles under them having conversations. It really serves to flesh out the personalities, which, unlike the general storyline, seem really well-developed and thought out. The one quibble I have with them is that the mouths seem to attempt to move at a deliberate pace, as if there was supposed to be speech accompanying the skits, as well as the music dying down. It gives this particular part of the game an unfinished feel, even if that was what was meant to happen.
The abilities that each character can learn are usually unique to them (with some of the abilities being split between various characters, but that's about 10% of the overall pool). Most of them have a charge time involved before being used, which requires either strategy or just plain luck in getting them to get pulled off before an enemy whacks you upside the face.
The other 3 party members that you have in your party are controlled by various settings that you can change regarding when and how much they use physical attacks, special skills, and where they use those skills from. The different combinations actually do produce different results from characters, and since one setting that works in one dungeon can get a character killed in the next, you will be spending some time configuring them occasionally.
The game gives you "Grade" after each battle, which usually deviates between -2.00 and +2.00 (it goes into the decimals most of the time). At the end of the game, when you activate the New Game + feature, you choose which parts of your previous file you "inherit" (i.e. keep over) by spending your Grade. If you don't have that much Grade, you might end up only getting your Special Abilities back... or if you want a challenge, you can make all enemies give you half experience the next time through. It's really a cool way to make the game experience different the second time around.
All in all, the game is quite enjoyable, and if you can look past the completely average storyline, a wonderful game is there for you to play, and enjoy.