Amazing, definitely won't dissapoint fans of the first game...
The story begins not as Sora however, but as a young boy named Roxas, and this serves as a set up for your character, a tutorial, as well as a re-cap of important events from the first game. After you complete certain things as Roxas, control will be transferred to Sora, and you will continue on.
There are several worlds in KH II, old favorites such as Olympus and Halloween town make reappearences, as well as new worlds such as The Lion King. Fans won't be dissapointed with the chosen worlds, and will be happy to see what Square Enix has done with this installment of the game.
Along with old worlds some old faces return. You will once again see an amazing cast of both Final Fantasy and Disney characters. Among the returning FF characters are Squall (Leon in the game), Aerith (Aeris), Cloud, and some others. Some new FF characters make the scene including Auron (FFX) and Tifa (FFVII). Obviously lots of the new Disney characters return, as well as some new ones, though I will leave those for you to see in the game. On a side note, some will find interesting is the return of Sephiroth (optional boss in the first game), only this time you see him in the story, and get another chance to fight him, and he is wicked hard once again.
Combat is pretty much the same, with one downside. The game relies heavily on button mashing. During battle you will see little triangles appear above your enemies heads, meaning you can perform special attacks. These are cool, but are used too commonly and make lots of the battles far too easy, but in a lot of battles it is worth it just to see the amazing feats that Sora and friends will pull off.
Another change is in the synthesis system. This time around you must find recipes or wait for items to be developed in free development before they can be made. Synthesis isn't essential to the game, and could be pretty much ignored and you would do fine, but to get everyones best weapons you must find the recipes and aquire the materials. Also the synthesis has a level, and each item will give the moogle experience, and everytime the moogle levels up you get new synthesis additions. It is worth it to turn in your items to the synthesis moogle however, because for everytime you complete a goal (such as aquire 10 different items, ect.) you will be rewarded with useful items, so even if you don't really like to synthesize, it is worth it to turn in the items you pick up.
All in all a very worth while game to pick up, especially if you were a fan of the first game. A little short for my taste (I completed it in just over 30 hours), but worth it none the less. I highly recommend this game.