I've recently picked up New Super Mario Brothers 2 on the 3DS, and there was a really interesting observation: A lot of stages now start with an "interactive tutorial" before the actual stage begins. Since it's kind of hard to explain what I mean, I've found a video of someone playing through it to show what I mean (at 2m 50s):
In fact, about half the stages I've encountered have shared this structure: A single static room with a tunnel that leads the player to the actual stage, with the level's most prominent "feature" shown. In the video linked above, it's the dynamically moving blocks; in later levels, other examples like giant man-eating fish, lava, and other course hazards show off what players should watch out for.
This, interestingly, is a dramatic turn from the previous standard that Nintendo has used with Mario games for quite some time now, beginning with Super Mario All Stars on SNES:
A simple visual that shows the type of enemy players will encounter in the stage. This is pretty much carried through to even New Super Mario Brothers on Wii.
The interactive introduction of the upcoming stage is an interesting design decision: when presented in isolation (and out of harms way), players can think and process the interaction at hand, and would be less surprised (and less likely to cry foul) with more later encounters on the stage. However, this does make the stage feel "choppier" and lacking in flow (stages all seem to be interrupted just as the player starts the stage).
Just an interesting observation.