Good game if you're a Kingdom Hearts fan. Otherwise...meh. Not bad.
Let's begin with how it measures up to the other PS2 games of the series and then go from there. The graphics were very very nice. No noticeable distortions, the monsters twitched and bounced and the cutscenes played just like they did on the console. I felt like I had the PS2 all wrapped up in my hands, minus the right analog stick, but the shoulder buttons worked just fine for turning the camera. It was a tad bit difficult to look up for stuff like collectibles, flying monsters, and areas to jump to. However, if such was really necessary, the SELECT button allowed a first person view.
The story was very nicely told, despite having to essentially play the game three times in order to figure out everything that happened. I did like how after you finish one game, there's an extra option in the main menu that starts piecing together how much you've completed in entirety of the game. While that was all good and dandy, clicking on any piece of the timeline brings up a lot of unnecessary text. Brief summaries would have been nice, and then the extra story bits available to be read somewhere else. Overall the story was moderately touching and had some interesting twists that fans of the series will definitely enjoy.
Now the music! The parts that were recycled from previous games were pretty obvious. They may have been sped up a little or changed slightly, but it gave a sort of nostalgic feeling as well as the "oh my gosh I remember this annoying melody being pounded into my head for hours" feeling. As for the new worlds, the music was either reminiscent of the Disney movie each world embodied or befitting of the new environment. Old sounds effects were familiar, new ones mildly amusing. The three different characters have their own unique fighting phrases, which added some nice variety.
Combat was very interesting. You really have to see for yourself, but I'll do my best to explain. You can do a normal attack with X, but you can also perform certain actions like special attacks and spells with the control pad and (triangle). These attacks and spells can be leveled up, and then melded to create newer and more powerful ones. Also, certain attacks trigger certain transformations and/or combo finals when a gauge to the side of the screen fills from getting hits. There's more and it all sounds very complicated, but when you've got the hang of it, it's quite fun and adds a great amount of variety to combat.
There are four difficulty levels. A secret movie is available as long as you don't play on Beginner, the easiest mode. I played on Standard and found most of the bosses to be almost disappointingly easy, although I did feel a bit of a challenge in the Mirage Arena (like the Olympus Coliseum in the original games) and with the final bosses. I remember dying a lot in the original games and having to figure out strategies to beat the bosses. Not on Standard mode in this game, so perhaps on one of the higher difficulties: Proud or Critical.
There's obviously replay value in that one needs to replay the story three times in order to get the whole picture. That was a tad annoying at times, but I think they did a good job giving each character's story enough variety to keep it from getting dull. Some areas are blocked from certain characters and open to others, and each character has their own bosses to fight and cutscenes to play in each world except for the few times they come together. There are also things to go back for in each game like trophies, challenges, mini-games, treasure chests, and collectible stickers. Seeing that 100% on screen is quite satisfactory.
Another few things that prevent the game from being monotonous are the Command Board, the Mirage Arena, and Disney Town. The Command Board is essentially a mini board game. It's complicated. I still haven't figured it out and won a game yet. You'll have to see that for yourself as well. I briefly mentioned the Mirage Arena earlier, but I thought I'd bring it up again just because it's actually the only part of the game I can't completely comment on. It has a multiplayer aspect which I've heard works brilliantly, but since I can't confirm or deny that, I'm just going to say that it's pretty fun even if you don't have friends to play with, which says something in itself. Then there's Disney Town. I won't go too into detail on that either, but I will say that it's like Traverse Town in that there are a couple mini-games to play and score on.
The last thing I probably want to comment on is the order in which you play. I played in the order: Ventus, Aqua, Terra. I liked this arrangement because the whole time I was wondering what the heck happened to Terra. Ventus is the one most kept in the dark, then I got a little more background and information from Aqua, and Terra answered all of my gnawing questions. I suppose it would also be appropriate to play in the order: Terra, Ventus, Aqua. The game has it lined up this way, and there aren't a whole lot of gnawing questions once you're through with Terra. I would advise against playing Aqua first though, since she tends to show up on worlds second or last, which is when stories on the different worlds are ending or surprises have been revealed.
Going back to my biased opinion again for a sec, I think the entire story was an awful, confusing prequel to the Kingdom Hearts series. A series that would have been fine without a prequel. However, it does explain some things, make both vague and direct connections to the PS2 games, and from what I've seen of Dream Drop Distance, sets the stage for that sequel as well. It's an absolutely great game by itself though, or at least one that hardcore fans of the series are bound to enjoy.