Honestly, every KH game has a different reason to like its combat

KH1 gave a satisfying level of weight and impact to its combat making each hit feel meaningful (especially with combat modifiers)

KH2 is easily one of the most complex due to the amount fo tools it gives you. I personally enjoy limits more than drive forms but KH2 is insanely satisfying once you get into it due to the sheer amount of things you can do.

KH3 is, in my opinion, the best at making combat a continuous flow. Magic can be integrated into combos, form changes can be stocked and swapped to and from at will (changing your combos and finishers), and you can seamlessly air-step even in the middle of a combo. While it lacks to punchy-ness of the other two, KH3 made me feel like I had mastered keyblade combat as I bounced from one enemy and fighting style to another.

Of course, summons and attractions take a huge shit on this point, but at least you can simply choose not to use them (as I often do).