A wonderful addition for the series that any player, fan or not, can't miss it.
The main character is Tidus, a professional blitz ball player. But, suddenly, in the middle of one of his games, a huge monster appears. A monster that will change his life forever. It called Sin, and, where it passes, it brings destruction and death. Also, it's through Sin, which Auron take Tidus and enter on it, making a travel to what's look like a distant future. This is how Tidus' history began.
Obviously, Tidus will eventually find some other characters and join them to help stop Sin, which still torment the world, even after (apparently) many years after the first time that it appeared. In total, Tidus will have six more friends. Each character has its own history, characteristics, abilities, overdrives, equipments and a voice. Yes, voice. FFX is the first of the series to use voice in conversations. Not all conversations, but almost all of them, even when, in English, they sometimes sound bad and weird.
And the best of the history is because you'll always stay wanting to know what come next, and some part of the history is told through amazing CG's, and any player know that Squaresoft (now is SquareEnix) have a extraordinary way to make CG's. In my opinion, these are the best CG's made for any game. In truth, any Final Fantasy game has them, and they're all of a flawless quality.
Like any normal Final Fantasy game, FFX have summons too, and they are called Aeons. The only ones that can invoke them are called "summoners", and only a few are trained in this path. Yuna is one summoner and daughter of the last "grand summoner" that fought against Sin, and Tidus have to protect and help her to achieve the same goal of her (and his too) father, helping to destroy Sin and bring peace to the world. So, Yuna is the only character that can invoke summons.
Also, Squaresoft bring some old summons to the game and uses new ones to increase the variety. You'll see Ifrit and Shiva in one way never seen before, and, in the same way, Bahamut is back, more powerful than ever. Also, the new ones have a nice concept and nice abilities, being a MUST that any player takes Anima and the Magus Sisters.
*EDIT: I didn't know, but, after a little reading, I discovered that the Magus Sisters aren't new in Final Fantasy world. Sorry about the bad information.
When Yuna summon one aeon, all other characters that are in combat will retreat and, the summoned aeon, will replace them in combat. But, the aeon will not just appear and release its overdrive and get out, no. It'll really replace and fight in place of your characters. The aeon will have health points, mana points, abilities, black and white magic, and can execute normal attacks and a special attack. Also, when the overdrive gauge is complete, it can release a powerful attack, the overdrive.
This works for the normal chars too, and any can use white or black magic, use any ability and other many upgrades on stats. And here is another innovation on Final Fantasy series: the Sphere Grid. Instead of gaining levels and upgrade specific abilities and stats for each char, you gain skill points. Each skill point allows your char to walk on the sphere grid, unlocking its upgrades, like magic, abilities and stats (hp, mp, strength, luck, defense, magic, etc). But, you don't must only stand or "walk" through one node to unlock it, but, you have to use the specific sphere to unlock it. Example: if you're standing over a +4 strength node, you must use a power sphere to unlock the strength node and increase +4 to char's strength. Ah! And you can also unlock nodes that are from one node of distance from the node that you're standing.
You may think that is a bad thing or that is an unfair level system, but, you're not free to "walk" to anywhere on the Sphere Grid. Some paths are locked with key nodes, which can only be unlocked with a key sphere, making the paths very restricted at the beginning, because the sphere grid have four levels of key nodes (level 1,2,3,4), being the level 1 easy to find, but, the level 4 key sphere, being a pain to find one. For example: to unlock "Ultima" spell, you have to use at least three or four level 4 key spheres to get it. Have to mention that empty nodes can be filled with other spheres, transforming empty nodes in stats nodes. This will be very useful, mainly after you start to visit the Monster Arena.
Ok then, back to the battle system. FFX make nice additions to it and really improve it. In combat, you can only use three characters, but, you can change with the others that are out from battle at any time. But if the character in battle is dead, sleeping, confused or under any other negative stat that make the char impossible to move, you can't change it for another. You must heal or revive it first to make the change. This time, the combats in turns is a little different than before, because, every action cost some amount of some type of "turn points". A "Quick Hit" skill, for example, will consume much less "turn points" than a normal attack, making your char able to attack again before the enemy does it; or do a overdrive will consume a lot of these "turn points", making your char delay for some turns your next attack. One little window appears on combat, showing to the player who will move or act in the next turns, so, you can chose the better action to do before the enemy attack or the better moment to heal your chars on combat.
Later, you'll unlock the Customize ability from Rikku, giving to the player a lot of possibilities editing your weapons and armors. And together, Final Fantasy X is the first from the series to give the player the possibility to break the HP and damage limits. When your weapon is able to break the damage limit, you reach a new limit in one single hit: 99999, instead of 9999. The same thing to HP, you can reach 99999 of HP, instead of 9999 (this upgrade is given through the armor). Of course that you can make others upgrades, like to give resistance, more HP, defense, magic attack, elemental attacks or effect attacks (sleep, death, slow, etc), combining at a maximum of four upgrade per armor or weapon. Remembering that you can change them in combat (armor OR weapon), but you spend a little of "turn points".
But I have to say that Final Fantasy X wouldn't be a Final Fantasy game if it doesn't had mini games and uncountable secrets. And I ensure you that Final Fantasy can make you easily spend a hundred hours trying to find and solve all these mini games and secrets, like special weapons, hidden aeons, stashes, overdrives, special events, special monsters, etc. Maybe you don't have patience to solve all this. I, for example, didn't have patience to make the "Dodge 200 Lightning Bolts" mini game. If you played it, you probably know what I'm talking about, about the pain, REALLY pain to finish this mini game… You can also play blitz ball later on the game. In my opinion, it's a boring mini game, and, at the beginning, the AI can easily own the player. But, if you wanna take the special weapon for Wakka and unlock the most powerful overdrive of the game (for Wakka too), you have to spend some hours here.
You have to be thinking yet about "woa! Do a 99999 damage in only single hit?? This is really over." If you had thought in this way, probably you didn't ever saw any of the "special" creatures from Monster Arena. There, a monster can easily reach the 1000000 (!!!) of HP and use multiple attacks with death effect or giving 99999 of damage in multiple hits. Or some others just counter attack with Ultima spell. Have to say too that, fight a creature that absorbs magic and is immune to physical attacks, isn't one of the easiest tasks on FFX.
For the graphics, I can only say that FFX is very beautiful for its time. Probably using all the power from Playstation 2, you'll see amazing light effects, nice textures, good animation and superb CG animation. The gravity spell makes a distortion effect appears around the enemies and the player; ice magic will froze the enemies, creating a realistic reflection and refraction from the ice; and much other effects that Square didn't let miss on FFX, looking out for all the details that they could use.
And, I can't let pass the music and sound effects. They're simple amazing! Why? Because, the one who made the composition of the sound track was no one more than Nobuo Uetmatsu, and no one doubt about his talent to compose amazing songs and melodies. Even the voices being of a mediocre quality, because of the bad acting, the sounds are great. All elements have nice sound effects: swords hitting its target, explosions, spells, footsteps; also, the menus have a nice sound too.
Well, probably I covered all the main aspects from this wonderful game that any fan from the series can't miss it. Even being very linear, the history justifies this linearity and later on the game, you can go to anywhere. Also, like any game from the series, FFX brings a new amazing and very detailed world, using a lot of power from Playstation 2, having a nice level design, being sometimes very surreal and fantastic (in a good way).