This is by far one of my favorite RPGs of all time and in my opinon one of the best.
You play Vahn, a young boy from a small village in a world scorn by a horrible mist that has rendered their way of life near useless. Now, after an attack on your village, you discover the Re-Seru, a special parasite that grants you powers and allows you to survive the Mist. On your adventure, you meet up with two companions with the same goal, and you soon discover more to your world.
That's the sort end of it. Unlike most RPGs, you only get two other companions. There's no mixing and matching players to your suiting. One balanced, one fast, one strong. Which is fine, because the combat system makes up for the lack of creativity that is lost in character department. Instead of choosing a simple attack and letting it ride, you have to give a combination of hits to deliver damage. Simply, it's up, down, left, right. Pretty straightforward, but those four directions make up a large arsenal of different combo attacks that deal out extra damage. The system is balanced as you get to add in more moves as you grow in level, and it wont let you do huge attacks every time without losing some Spirit, the third party in the MP HP party.
Speaking of MP, your magic is based around collecting the spirits of element based monsters. Each time you pummel them into submission, you have a chance to pull them into your parasite and use them for later (my favorite is the flaming kamakazie). They dish out major damage, so of course use them sparingly as they cost a bit of MP.
The story is great and does change depending on your actions. So there is alot of replayability.
There is more depth in this game than you think, but I'll let you find that for yourself. :)
You can pick this game up for about $20 tops now and it's well worth it if you're an RPG fan. Pick it up, or I'll throw a brick at you. :D