In order for Kingdom Hearts 4 to break out as the next best game in the series, it will be best to look back at the successes of every game that has come before. This should include the designs that help Kingdom Hearts 3's worlds excel individually over many other locales introduced across the series.
Specifically, the successes of Kingdom Hearts 3's world-specific gimmicks could help ensure that Kingdom Hearts 4 is able to rise above older entries. The most notable game to overcome would be Kingdom Hearts 2, which is often considered as the best title so far for its combat and bosses, even though it struggles at times to give its locations unique gimmicks that make each world stand out among the crowd. It should also be noted right away that while "gimmicks" can have a negative and forced connotation, the following will be using the term to describe unique mechanics that are only present in limited areas.
Kingdom Hearts 3 Ties Gimmicks Directly into Combat
The way Kingdom Hearts 3 succeeds most with its world-specific gimmicks is in how these unique mechanics are integrated directly into the basic combat of a level. Notable examples of this world-specific combat include the Gigas from the Toy Story-inspired Toy Box and naval combat onboard the Leviathan and Black Pearl in The Caribbean. While both of these concepts heavily impact combat, they are only available in the worlds they appear in despite potentially enhancing other levels.
This reworking of combat from world to world could make gameplay feel inconsistent, but in Kingdom Hearts 3 this design philosophy makes every world liable to be somebody's favorite. Making the combat in each world so different from the others means every new trip on the Gummi Ship goes to an exciting new location that will have a fresh take on the base mechanics. As Square Enix moves toward developing worlds that will stand out in Kingdom Hearts 4, it should make sure that the combat has meaningful changes across all levels.
Kingdom Hearts 2's Underwhelming Mini-Games
On the topic of looking back at the successes of previous games in the series, it should also be noted that Square Enix is listening to fans by reintroducing the reaction commands from Kingdom Hearts 2. However, there is a danger to looking at the way that Kingdom Hearts 2 is often ranked as the best title among the series, especially when it comes to this game's gimmicks. More often than not, the changes from world to world for Kingdom Hearts 2 came from mini-games rather anything that altered the actual combat.
These mini-games run the gambit of interesting to tedious, with some of the better stand-outs including guiding Minnie Mouse in Disney Castle, while the worst examples include pushing the Wardrobe in Beast's Castle and the Demyx boss fight's Dance Water Dance. The worst part about these gimmicky mini-games in Kingdom Hearts 2 isn't even the lack of combat integration, but the way it cuts the pace of gameplay short to solve an uninteresting puzzle. With that in mind, Kingdom Hearts 4 should avoid relying so heavily on making mini-games mandatory obstructions, and instead lean on making worlds excel through unique combat.
Fortunately for Square Enix, the Kingdom Hearts series has a lot of successes to iterate on in order to improve the experience jumping into Kingdom Hearts 4. Additions like Flowmotion and Shotlock during the handheld era between Kingdom Hearts 2 and 3 have only enhanced combat and made enemy and boss encounters more impressive and fast-paced. Similarly, drawing from mechanics in early Kingdom Hearts titles could go a long way toward making this the true culmination of everything the developer has learned.
Kingdom Hearts 4 is currently in development by Square Enix.