Hm...

For the graphics, a beefier version of Wario Land: The Shake Dimension is the first thing that comes to mind. I'd prefer a hand-drawn look over 3D graphics like Donkey Kong Country: Tropical Freeze has them. The soundtrack should have much more variety than in the NSMB games, but that's something that should be obvious to everyone.

All those world themes that were in Super Mario 3D World and Super Mario Odyssey should be present and more. Nintendo used the same eight in all four NSMB games despite sitting on a huge pile of other themes that could have been used. New enemies and especially new bosses.

Gameplay and level design have been stellar in the NSMB games, but the rest has to be lifted to the same level. That's basically it. It's something that Nintendo refused to do when Shigeru Douchebag Miyamoto was general producer. His mission was to make 3D Mario games sell better than 2D Mario ones, so new ideas and production values were reserved for 3D Mario to convince the market that 3D Mario is the superior Mario. However, the influence that those decisions had on sales were first and foremost a reduction in 2D Mario sales while 3D Mario sold hardly better than before, so the mission failed because significant damage was done to hardware sales by handicapping a big system seller IP.

If Furukawa wants to demonstrate that he has a clue, he will tell the developers to make a 2D Mario game as good as they can because the market (read: the historic sales data) demands it that way. Whereas Iwata was both a developer and businessman, and therefore his developer roots made him sympathize with developers too much at times, Furukawa is only a businessman and should therefore tell the developers who is the boss. The market is the boss. If Nintendo wants to continue to sell lots of hardware and software, they'll have to serve the boss. That will be Furukawa's big challenge, that he keeps his best developers in check and doesn't allow them to make Sunshines, Wind Wakers and Pikmins.

Gameplay and level design have been stellar in the NSMB games, but the rest has to be lifted to the same level. That's basically it. It's something that Nintendo refused to do when Shigeru Douchebag Miyamoto was general producer. His mission was to make 3D Mario games sell better than 2D Mario ones, so new ideas and production values were reserved for 3D Mario to convince the market that 3D Mario is the superior Mario. However, the influence that those decisions had on sales were first and foremost a reduction in 2D Mario sales while 3D Mario sold hardly better than before, so the mission failed because significant damage was done to hardware sales by handicapping a big system seller IP.

If Furukawa wants to demonstrate that he has a clue, he will tell the developers to make a 2D Mario game as good as they can because the market (read: the historic sales data) demands it that way. Whereas Iwata was both a developer and businessman, and therefore his developer roots made him sympathize with developers too much at times, Furukawa is only a businessman and should therefore tell the developers who is the boss. The market is the boss. If Nintendo wants to continue to sell lots of hardware and software, they'll have to serve the boss. That will be Furukawa's big challenge, that he keeps his best developers in check and doesn't allow them to make Sunshines, Wind Wakers and Pikmins.