The game was fundamentally shallow
http://iwataasks.nintendo.com/interviews/#/wiiu/splatoon/0/0
For example the Iwata Asks interview with the Splatoon team mentions that the early prototypes for the title were just experiments where boxes were running around in a box world shooting colours at one another. Once that was fun and the controls felt good they figured out everything else about what the game was going to be.
Your comment seems trivially true to me. How can one possibly begin the second without the first? And yet people try it all the time!
Plenty of games are created by jumping right in and starting to code, and then seeing where that takes you. For example, the throwaway game that inspired Portal.
Of course, eventually you do have to take periodic breaks to review things and plan the next phase.
In today's industry an overlook like this might be useful in level design but I can't really see it having a big impact on the actual development of the gameplay as long as you know what actions the player can perform you don't need to know where they are going to be placed or what they will look like.
For example: If I say "Oh, it would be really interesting if there's a Dungeon of Reflection in which the entire dungeon is symmetrical, and the monsters always copy the character's movement", then that would require some careful level design, which having worked out, could translate into a mechanic.
Operating in reverse is much more difficult and ends up stuffing mechanics into a sense of play. "It's easy in code to make the character teleport! Now.. what should we do with this?"
Edit: I was also hoping there would be an album or collection of the Zelda assets - is it just the embedded ones on the page they released?
on the other hand, I've been subject to one surgery and been third-party to multiple others, and can't see how this isn't true.
One of the things we often lack in software is a good medium for exploring mechanics. Getting something to the point where we can conduct an "Is this fun?" test or more generically "Does this serve the purpose" without a massive development undertaking.
A medium? Would you care to expand on this point? While I agree that more work could be done on speeding up the tools used, the process / concept / activity itself already exists, so I am not sure what you mean by medium.
PROTOTYPING is a fundamental part of the software engineering process (and other engineering disciplines), but I see it get missed A LOT in software development, for a variety of reasons. https://en.wikipedia.org/wiki/Software_prototyping
As vvanders has already said, "White Boxing" is a common technique for video game development.
On the BG Planning Sheet, 年 月 日 mean Year Month Day -- for indicating the date. 時 分 are Hour Minutes -- for indicating the time. デザイナー means Designer and プログラマー means Programmer.
Oddly, the last page seems to be a mirror image, and it's quite difficult to read the text. However, it appears to be for designing an individual sprite. There is a field labelled キャラクター (Character) along with Date and Memo fields.
Chris Taylor used to say the "game is the design document." There is obviously a lot of problems with that approach. But I have also seen terrible results from teams who plan on paper and neglect the reality of the work product.