Kingdom Hearts was an okay game, and in retrospect, I'm not sure what all the fuss was about.
Remove the unusualness of Disney characters in a Square RPG, and what you get is a very simple button mashing experience. That's all the battles are, by the way. Button mashing. "Combos" are accomplished by mashing the X button a little faster than normal. Magic is close to useless, as your MP runs out before you're able to destroy anything but the weakest normal enemies.
Your comrades throughout the game are Goofy and Donald. Donald is pretty useless. He can take out large groups of weenies pretty quick, when he's around 10 levels higher than he has to be, but other than that all he does is take hits and use potions. Goofy at least takes a LOT of hits, and is quick enough with the potions to keep you healed without you having to do much. Which is good, considering you really don't have time to do much as you are the only one doing any real damage at any particular time, and the fights go at a frantic pace. You have the option of using other characters every once in a while, but all that really does is deprive your main characters of experience, considering you can't take the extras with you from world to world.
The camera is horrible, as I'm sure you've heard elsewhere. It's impossible to look forward if your back is to a wall. I guess because the camera can't fit back there? It swings around wildly when you're fighting something big, for no apparent reason, and sometimes doesn't swing at all when you desperately need to look at something. You can adjust it manually, but it'll just go back to where it was, be it on automatic or manual mode.
The story is pretty good. It moves rather quickly and makes the game go by pretty smoothly. There's not much side story or character development, but then again most of the characters are rather nonsensical anyway. Take, for example, the fact that Tidus, Wakka, and Selphie start on the same island as Sora, the main character. And they're all kids. If you know anything about the Final Fantasy stories, you would know this is not only impossible, but quite silly. It seems to me that characters from previous Square games were only thrown in to sell the game, as their character stories are never used...they basically become different people entirely with no mention of their previous histories in the other games.
The music is ok. Actually it kinda sucks. Although there's nothing particularly bad about it, there's absoloutly nothing good. I'm a very musically oriented person, and not once did the music make me think "that sounds good." In fact, it was muted a few times just because it's very repetitive.
The graphics are good in their cartoony way. There isn't really much content as far as places to go...there are about a dozen worlds (not sure of the exact number) and each one has, on average, about 10-15 screens. That's it. Not much in the middle space besides the stupidly easy and SNES-looking Gummi Ship levels that are between worlds.
And speaking of the Gummi Ship...what the crap was that? This game should be rented at least once just to experience the sheer stupidity of the Gummi Ship levels. And don't bother upgrading your ship unless you just want to...those levels will never get hard. And you'll be amazed how many times you work hard to get to a treasure chest that's in some wierd place that requires all manner of jumping at wierd angles and from platform to platform, only to find it's freaking Gummi in the chest. Whoopti-doo.
As a side note, although I was poised to go through the final world, I did NOT defeat the final boss. Why? Because I was quite tired of the game already, and really wasn't in the mood to "fight" (read: press X with a vengeance) a final boss with the camera going all stupid and having to jump on his back so you can actually hit him or whatever other nonsense. I might go back when the sequel comes out, just so that I can decide with a clear head whether or not I want the sequel. Odds are, I won't.
I suggest you rent this one before you buy it, though the greatest hits price of 19.99 might make it worth it to just go ahead and buy it and take your chances. But unless you're a big fan of button mashing action games, you're not going to like this. The story carries it enough to be played, but not enough to make it worth buying over many other RPGs, and the addition of the Square characters was a good idea, but it doesn't seem fully implemented.