The fourth game in the series and the 3rd game and thankfully final game which reuses a bunch of stuff from kh1. Despite being a spinoff ds game which doesn't have much bearing on the overall plot it actually has some well thought out mechanics which make it worth playing if you enjoy kh. It has a cool version of birth by sleep's command deck system where you can fuse different moves together to make one stronger, though getting new moves can be a bit finicky. I also thought that the motherboard where you upgrade your character by putting down chips like levels, strength, and resists was a really good idea. It even has a bunch of setting which let you control how strong enemies are for certain rewards like more money or exp. It fit the aesthetic of the game really well and actually functions as well as it sounds on paper. Though the graphics and sound are completely fine they obviously don't match up to the other games, which makes the repetitive killing of heartless and bugs not the same as the satisfying kh1, kh2, or even CoM. It makes up for it's gameplay not being able to rival it's brethren by adding a lot of variety into the gameplay. There's even a turn based rpg resembling super mario rpg which is actually pretty fun, though a bit easy even on crit. Even despite these breaks from the gameplay I still found myself a little bored of the repetition of not only the worlds being the same as kh1, but the mini dungeons you have to do in order to proceed which all look the same and have one boss which appears sometimes. I think the boss battles are actually surprisingly fun though, all very well designed with very punishing attacks that are very feasible to dodge. Even though I felt underleveled I never felt that any boss was impossible. The game even has a lot of extra content to do after the final boss which is not something I could even say for CoM.
The story isn't really worth talking about, though I did actually like the dialogue a bit more then I did in 1 and 2. Plot doesn't really make that much sense and is used as a way to revisit worlds from kh1 and CoM. If this game were put on a console, and was a bit longer I could easily see it being a great game. I think that a lot of decisions made in this game show that a lot of thought was put into how to make it interesting with what they had to work with. However due to limitations of the console and it being pretty irrelevant storywise it's just a bit better than average in my opinion.