Let's talk about Kingdom Hearts level design.
Inspired by this:
http://www.gogglebob.com/2015/09/12/kingdom-hearts-faq-10-cowardly-level-design/
as well as marathonrecaps'
Kingdom Hearts retrospecitve posts.
The latter blogger thinks that Birth by Sleep is "flatter" than KH2, amazingly enough. I don't comprehend why he thinks that.
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OH BOY MY TERRITORY
I only glanced at the posts since they're pretty long and I'm already pretty in touch with what they are talking about.
But basically, KH1 remains the only game in the series to have strong level design all around. There is an emphasis on exploration and platforming, and there is a lot of interactivity within the worlds, and a lot more moving parts. It makes the world feel more alive as a result. KH1 is the game in the series that focuses more on the little things than other games in the series, which might be the result of it having a humbled development (they knew that having this Disney/Final Fantasy collaboration was a big gamble, so they didn't go too over the top with things in this game). This is a large part of why the original game (or it's Final Mix version, which is just strictly better), is my favourite game in the franchise and one of my favourite games of all time. I still discover new things about the game every time I play it. Usually just small things, like a secret item (like when I found out you can FREEZE THE BUBBLES IN HOLLOW BASTION WITH BLIZZARD TO MAKE PLATFORMS AND IT GOT ME A CHEST THAT HAD ME SCRATCHING MY HEAD SINCE I WAS A KID LIKE WHAT?), a new strategy for taking out a boss much easier, or just general easter eggs (I actually never noticed the Lady and the Tramp statue in Traverse Town when I was a kid, I only noticed it when I played the PS3 remaster). It's one of the few games I'm actually interested in getting into full game speedruns of as a result. It's a game I always enjoy coming back to and the varied and intricate level design is a large part of why. Granted, it's certainly not perfect all of the time - the platforming mechanics and camera are dated (though I've gotten used to it so it doesn't bother me these days), and there are a few areas with poorly placed enemies where fighting is just really awkward, but most of the time, the level design in KH1 just makes the game feel more exciting and wonderful to play through. For first time players, each new room you visit is a surprise, a challenge in itself even if you aren't fighting enemies, with the platforming and puzzles to do and the secrets to find.
When it comes to other games in the series though, the level design takes a back seat. KH2 is a fantastic game, especially the Final Mix version, but as good as it is, I feel like it failed it's job as a sequel - to improve on every major aspect of the original game. While it definitely improves on many aspects (Sora is obviously much more fluid to control, for example, and they added loads of extra combat options and boss fights in general are more action packed), it heavily, HEAVILY nerfed the level design most of all.
See, when I think back to what made KH1's level design so amazing and revolutionary to me as a kid (and why I still enjoy it), I come to one point - the fact it was an RPG, yet it was also felt like an action/adventure/platformer game. In most other RPGs (exceptions existed, like Paper Mario), your field experience was moving, talking/examining, and nothing else. You might get the odd "auto-jumping" sequence or something but that was it. Battling and exploration were two completely separate experiences. KH1 flipped that mentality on it's head though and merged the two experiences together, by integrating the two aspects of an RPG. You had sections where you had to fight enemies while paying attention to your footing. You could purposefully lure enemies into more advantageous spaces to fight them. You could run from fights like in other RPGs, but this time, enemies would chase you down through the environment. Healing up meant you also had to make sure you weren't left wide open while doing so. And your magic spells didn't just serve to work in combat, but also to enhance the experience of exploring the world - you could use them at any time so you could try your spells on different things and sometimes you'd be rewarded for it.
KH2 though? They regressed all of that. While enemies are still technically integrated into the world (i.e. you don't get dragged into a "battle screen" to fight them), fighting and exploration don't feel integrated because enemies usually only show up in very obvious "arenas" that you can see, and most of the environments outside of that are still pretty much flat corridors. While KH2 may give you more INNATE combat options, it's literally just you and the enemies (and Dolan and Gooby). No longer is there any strategy related to your terrain, enemies can no longer surprise you when they show up since that's basically all there is to the worlds anyway, and you don't have much to do outside of fighting (Final Mix remedies this somewhat, but not completely). KH2 both regresses to the primitive PS1 Final Fantasy days of "walk to fight to walk to fight", and ironically, loses a lot of the RPG elements in the process - it may as well be a pure action game with lite-RPG elements. And while it's a damn good action game, I feel like it lost some of the charm and uniqueness of the original (even more so when we consider the story, but that's a whole other kettle of fish).
What's most odd about this, is that in KH2, Sora controls like a dream - get a few growth abilities on him, and Sora's movement options and fluidity would make actual 3D platformer characters like Mario, Crash, Spyro, or Rayman jealous. This is emphasised so well in the Final Mix exclusive Cavern of Remembrance, which feels like it was made for the people disappointed in the lack of exploration, puzzle solving, and platforming in KH2 (there's also the Puzzle Pieces they added throughout the worlds). It's just so odd that they didn't design the rest of the game around this - for some reason, getting these growth abilities is entirely optional, so they designed the world to be pretty flat so you can get through the game without them. However, KH1 did make it possible to complete the main game without High Jump and Glide too, but it did so by adding intelligent ways for you to still traverse the mandatory areas if you chose not to use them, without sacrificing interesting level design ideas. For example, remember how I mentioned the ability to freeze bubbles in Hollow Bastion using Blizzard, turning them into platforms for a few moments? Well, in the vertical canyon areas of the world, where you need to make your way up to the platforms to get to the castle, most players should have High Jump and Glide by that point, so they can pretty easily make their way up. However, if for some reason you don't have those abilities (which is possible), or decided not to equip them, you can still make your way through the section by freezing the bubbles to make up for your lack of a higher jump. This gives players the option to not use High Jump and Glide, but still able to make it through every world and to the final boss without sacrificing the interesting level design. KH2 doesn't doesn't even bother with this, and instead just makes everything flat and boring, because god forbid someone have to THINK about how to progress from point A to point B, lest they decide the game is bad because they couldn't fight more Heartless every two minutes, and decide to trade it in.
Since then, most other games in the series have maintained a pretty similar level design mentality. Birth By Sleep had echoes of what we saw in KH1, but it was still pretty flat and boring (and unlike KH2, the combat and boss design is pretty bad now, so it's my least favourite game in the series because of that). DDD had Flowmotion so there was more verticality to the worlds, but because Flowmotion is so over-the-top, you don't have to think about how you get from once place to the other, you can just wall jump up almost everything (and I mean a single wall, like in Mega Man X - except Mega Man X is designed around that mechanic to prevent it from feeling overpowered, while DDD is not). This is especially evident when exploring the three districts from Traverse Town that are in DDD that were previously in KH1 - they feel so much smaller, and there's no satisfaction to exploring them (and all of the interactive elements are gone - you can't even go inside that little café in the First District, it's blocked off by an invisible force field). 358/2 Days and Re: coded actually DO have quite a bit of platforming and exploration but are held back a bit by the DS hardware (Re: coded is still my favourite game after KH1 and KH2 though).
If 0.2 BBS is any indication though, KH3 will be bringing back the more varied world design of KH1, except expanding the scope of it greatly, as well as the players movement options. While I still have my concerns about performance optimisation and the combat of KH3, I am really excited about how the game's worlds look to be really fun to explore again.