An inspired combat system and excellent premise are dampered by average storytelling and forgettable characters.
You have not one, but two leading men. And I don't mean two guys in the same party; you actually switch back and forth between two (mostly) separate storylines throughout the game. Predictably enough, the fates of your two parties are quite intimately intertwined. And that really sums up the story: predictability. They establish a nice baseline for the story to get really interesting, then proceed to take absolutely no chances with it, both with the events and the dialogue itself (which is a veritable dictionary of cliches).
Fortunately, the splitting of storylines does wonders for an already stellar turn-based combat system, which is both intuitive and strategic enough that it always stays interesting. The basic idea is that each character can move a certain (varying) amount around a 3-dimensional battlefield each turn, and can attack once. Each character has vary attack ranges and breadths... for example, one character wields a rather large axe and can hit a short but wide area in front of him, making him excellent for crowd control. On the other hand, there's an archer who can eventually be made to fire arrows through lines of enemies, so if the stars align, you could be hitting 4 enemies in one shot.
If that doesn't already sound interesting enough, keep in mind that you'll be cutting back and forth between two different parties with different strengths, and the game makes a conscious effort to vary the terrain on you to best take advantage of the strategic elements of the game (height bonuses, attacks from behind, lining up enemies for multi-hit attacks, etc). I found my deimos party to be stronger in general, and more suited for short-range combat. While the human force was generally a bit weaker, the archer became almost laughably dominant after a bit of leveling up. Speaking of which, even if you're not the leveling-up type, you may find yourself doing just that simply because you legitimately enjoy the combat. Never does this game reach the point where you feel there's too much combat, and there are even a few "arenas" for those who want a little more challenge and extra goodies.
The graphics are fairly standard PS2 fare. The music is generally either very pedestrian or strange stuff that makes you wonder what they were smoking (not quite Xenosaga 2 bad, but still just... weird).
Overall, if you want to check out a great combat system, give this a try. If you're looking for a good story though, there are any number of better things out there.