Mostly fun, but a few oversights leave the player frustrated
Graphics: Pretty good, and they definitely stand up today. The CGI cutscenes are still great, and the character models are well designed and don't have many jaggies for a 2002 game. However, I noticed one problem that annoyed me throughout the entire game. The lips of the characters were dubbed from the Japanese release, so the lips don't match at all, and they look VERY obvious. If you've seen any Japanese dubbed action movie, you'll know what I'm talking about, but multiply that by 100 and you have the dialogue from KH. But otherwise, the graphics aren't terrible, and are certainly viewable even today.
Gameplay: This is the main category for the game, and the most important. Let's start with the battle system. I haven't played a FF game for very long without getting bored, so forgive me if I make a mistake here, but I'm pretty sure the combat system isn't like FF. So, instead of turn based combat, you have real time action. This is more involving and more action packed, and I can see why they made the decision to go with that system (probably to differentiate it from a FF spin off and to make it kid friendly) Battles aren't TOO hard, but they aren't very easy, and I can see a kid getting frustrated with this game, despite its E rating. Combat can be a little difficult in some ways, but as long as your teammates are well equipped and have some potions, you'll probably come out alive. One of my main issues is with the environments though. I'm looking at this game through an eyes of a 10 year old, perhaps, and I can see the pathfinding being way too difficult without the help of the guide (which doesn't help much; I have it, and it's not really good). For instance, the player must push aside a bed in Wonderland while they are tall in size to allow themselves passage as tinier beings. You get no warning of this, however, and if you drink the tiny potion without knowing this, you're basically stuck. In Tarzan's Deep Jungle world, you have to rescue 5 gorillas from the evil Clayton. Are you given any notice of where these guys are? Nope, you have to find them yourself. For a game advertising Disney related media, the game can be a bit kid unfriendly. One last thing. To travel from world to world, Sora, Goofy, and Donald must fly in the Gummi ship through space, and blast enemy targets. The system is a huge annoyance and letdown, and feels VERY half baked. Basically, you fly a little ship that shoots a laser through weird blocky/gummi type areas while going through rings that revolve. It's all very out of this world (excuse the pun), and while it adds more gameplay, it can be annoying to have to go through it EVERY time you want to get somewhere.
Story: Pretty good. I don't want to spoil the whole thing, but I'll give you a few key points. Your guy, Sora, lives on the Destiny Islands with his friends, and they start building a raft to get off the island. One day, the Heartless attack, and Riku is lost to the Darkness while Kairi is nowhere to be found. Sora is thrown into Traverse Town, and meets up with Donald and Goofy in their quest to find King Mickey. Sora wants to find his friends, so they team up together, and go from world to world, battling the Heartless. It's not a great story, and while there are a few unexpected plot points, it's not gonna make you cry along the way.
Sound: Very good, the orchestral soundtrack definately is innovative and doesn't just use Disney music. However, some of the tracks are repeated a lot, especially in certain worlds, so it can get a bit repetitive. On the other hand, it's good music, so it's not like you're listening to crap.
On the whole, Kingdom Hearts is pretty good, but I just couldn't get into it.