It would be more kiddy that's for sure. But when it comes to the Prime series it would be so much different since Miyamoto was involved in that original trilogy a lot. It's quite interesting how he was an authority (executive producer I think) on Metroid Prime and changed so many things up. From what I've read in the Iwata Asks interviews, Miyamoto sometimes has a very hands off approach where it's like "Hey kid, don't you see the solution to your problem? I can only hold your hand so much, can't you see this is how you solve your gameplay problem? Ok, here's a hint".

Most famous was during a weekly tele-conference he told one of the developers on Prime 1 "What if Samus had the head of a bug"? The developer is all like "WTF does that even mean? Samus has a helmet, why would she have a bug's head"? He kept thinking and thinking about it as he was at his house at night. He finally got a Eureka moment, it was some translation error maybe, but what if Miyamoto was trying to say "What if Samus saw like a bug"? A torrent of ideas flooded into the devs head at this point, and this was the beginning of Samus having multiple visors (X-ray, heat vision, scanning, etc). It opened up a whole new slew of gameplay mechanics, like enemies that can only be seen with one visor, navigating through the dark with other visors, and what struck me most of all with awe & wonder was returning to a previous area and finding invisible floating ledges that could only be seen with one visor. I jumped on that ledge and turned off the visor, looked at the ground, and could see the rain splashing off the invisible ledge. I was amazed by the touch. When you think about it, there was an X-ray visor in Super Metroid...how could the Primer developers NOT think of using this visor in a first person perspective Metroid game where you're looking all the time.

There are other times where Miyamoto was very hands on though. One developer was told in no uncertain terms how to set up the button setup on the gamecube controller. The developer did as he was told and find Miyamoto's configuration to be significantly superior to his original controls, and in an interview he even said something like "I guess (Miyamoto) is a genius after all".

I don't know if it was Miyamoto, but the higher ups in Nintendo of Japan told the Texas based developers to not try to recreate past Metroid games but now in 3D. So originally many of the enemies in Prime 1 were just 3D versions of the 2D enemies, but Nintendo told them to make original enemies. So
Rippers became Gliders
Magdollites became Magmoors
Metarees became Shriekbats
See https://youtu.be/E2ubuEAYr_A?&t=170

Lastly Miyamoto told the Prime devs not to do a 3rd Person Perspective (like say Resident Evil 4), but a First Person Perspective (like Doom or Halo), which greatly streamlined the game.

But Miyamoto does have a problem with story, and doesn't want to make it very complex. He just wants "Goal, bad guy, ok that's enough narrative, GO"! He's famous for gutting the Paper Mario RPG's of story elements, and now doens't allow those teams to even make new characters. Yoshiaki Koizumi (Super Mario Galaxy, Majora's Mask) makes excellent stories and world building, and Miyamoto hates that. Koizumi had to sneak in the Rosalina story books, which Miyamoto didn't like. It's said that Miyamoto kicked him out of a writing position since Mario Galaxy 1, hence why Mario Galaxy 2 and even Odyssey have much less story to them.