Kingdom Hearts 1 is my favorite game of all-time. Yes, I am a fanboy--but I really do have reasonable support for my claim. I love Final Fantasy, and I love Disney...so it is to be expected that I'd be all for such a game that combines both elements.
The combat, though repetitive, is quite addictive, and I'm a sucker for high levels of customizable options. You can tune yourself and your party members in so many ways as you collect and synthesize powerful items and equipement.
Also, the story is rather addicting. I thoroughly enjoyed visiting the various Disney locales and fighting alongside its respective hero...as well as against its respective villain.
The playability is top-notch. Very easy to execute attacks and dodge opponents. However, I do not favor the method of which they force you to use items, magic, and summons. Scrolling through menus while in the heat of battle is tedious (though, the quick magic menu is a huge aid).
Now, for some complaints. After all, no game is perfect. Kingdom Hearts 1 is way too easy...so easy, in fact, you can beat the game with the smallest of efforts. You can complete the game without dying easily. Also, the gummi ship aspect is absurd. The graphics are a disgrace to an otherwise respectable looking game. In addition, the gummi ship is just plain not fun.
Still, that is hardly enough to hinder the Kingdom Hearts experience. If you have yet to play this game--then play it. Decide for yourself if you like it or not, but play it.