The following is just my opinion.
This game can be tough. Not because of well thought out puzzles, difficult enemies and bosses, but because of design flaws.
The camera will fight you during battles, often looking to the sides of your enemies rather than keeping them centred.
Late game fights get drowned in enemies, most of which will fly off away from the camera whilst their friends barrage you with ranged attacks you won't be able to anticipate. If you don't spend a lot of hours grinding for levels and equipment then you just aren't going to make any progress, so if grinding isn't for you or you don't have the 30 + hours to sink solely into your character then you're better off trying a different game.
Some of the level designs are simply wrong, with some locations, notably Hollow Bastian, having messed up geography that is easily noticeable and immersion breaking.
Boss fights are either easy or ridiculously difficult. A number of bosses will go down in a few hits from particular spots on the level. Others will take you out in just 2 or 3 attacks, a particular few bosses having undodgeable attacks which are never a good idea.
The biggest praise this game can receive is in regards to its soundtrack. The many Disney themes are nice, to begin with, but you will likely be tearing your hair out after listening to them on loop for each location you visit because somehow it was considered a good idea to have one song and one song only for most levels. Instead, the original music created for this game triumphs as the games only value.
Characters are a mess. Memorable appearances from the Final Fantasy franchise are completely different from their source material, even changing Squall's name to Leon and raising Aerith from the dead. Most Disney characters do not play a large role aside from Donald and Goofy, taking the role as set dressing more than anything else. The story of Sora, Riku and Kairi can be genuinely engaging at times and helps to keep this game in higher regard than the rest of its elements deserve.
The method of travelling between the different worlds is utterly baffling. The Gummi ship section is completely out of place with everything else in this game. It almost seems like a developers son or daughter began coding games and convinced their parents to put their work in one of their games because it just doesn't fit. Coincidentally it isn't entertaining and you will reach a point where you don't want to travel to a new location because you know you're going to have to go through that mess again.
Overall this game does not live up to the praise it's gained since the release. Maybe you need to be a hardcore Disney and Final Fantasy fan, maybe you need to have played it when it first came out, but today it isn't worth playing.