"If the next Mario game is 3D (which I think it will be) I want it to return to the original platformer design of having several levels (like 50 or so) with one goal each: beat the level. Ever since Super Mario 64 every platformer only has like ten levels and the goal is to collect a bunch of stupid crap. Back in the glory days of Mario platformers like Super Mario Bros 3, Super Mario World, and Yoshi's Island each level only required you to get from one end to the other and everything had a more action based approach. Sometimes you had levels that had a secret exit (that usually would unlock secret levels) or you would have a boss battle."
This isn't an entirely new idea - games like Crash Bandicoot have done it. Still, I have long awaited a Mario game in this format. That's not to say I want it to be like Crash Bandicoot gameplay - I just want it to have a similar structure for progress.
The alternative, I think, is to go the other way - MORE free-form and explorative in nature than SM64 or SMS. Instead having individual levels and events, have one huge, open world. I found that it very irritating in SMS when a particular event would only use half of the level. Why not combine them all and let you tackle whatever Shine you want in any order? I'd much prefer that to SMS's half-linear structure.
So, in other words, I want Nintendo to either be completely linear, or completely non-linear. Either would be great, but I'm tired of the SMS format.