During the 3D renascence of Mario titles, it seemed like there may be no return to the portly plumber's 2D platforming roots, until the Nintendo DS saw the release of New Super Mario Bros. This game took an opportunity to "return to form". But simply going back to the hallmark that was Super Mario Bros. 3 would only end badly. People would always compare them, saying that NSMB was just a copycat and Nintendo was getting stale. So something had to be done to make the game feel separate from its fellow titles. How did they do this? By clipping its wings...literally.
New Super Mario Bros. was grounded. There was no flight in the library of power-ups. Rather, the game focused on size manipulating mushrooms that could make one either very big or very small. This changed how a player explored the level. In most 2D Mario games, secrets tended to be discovered by going off the map. You might leap above the ceiling blocks to run to a warp zone, or you could fly up into an otherwise hidden location. But in NSMB, the secrets were right under your nose. Miniature tubes, too small for regular Mario to climb into could be found on levels where the mini-mushroom wasn't even available.
This added an extra layer of challenge. In most Mario games, power-ups do exactly as their name suggests - they "power" you "up". However, the mini-mushroom was both a blessing and a curse. It let you jump higher, fall slower, and fit in smaller spaces, but you were just as vulnerable as in your starting form. One hit killed. Secret areas and entire worlds were only accessible if you were willing to keep yourself in a constant state of fragility.
This one item made a world of difference to gameplay. Look at other power-ups, in Super Mario World there was secret area behind an early ghost house where the player could get two fire flowers, two feathers, and a Yoshi. No one ever picked up the fire flowers. The feather allowed a player to fly, spin-attack, glide with Yoshi, and find any secret area. Players only picked up the fire flower if they couldn't get a feather, and really there was no need to have the fire flower in the game at all.
In New Super Mario Bros., the fire flower was my default mode. It was what I needed to survive a tough encounter. But by sticking to the fire flower and keeping my power, I was losing the chance to explore all the nooks and crannies of the game. I was even missing out on whole worlds I could be exploring. To get to those places, I needed to sacrifice my power and put myself in a perpetual state of weakness. The mini-mushroom didn't make levels easier. It made them more exciting, because I was suddenly so weak compared to my previously flame spewing, three-hit surviving self.
By coming back to earth, New Super Mario Bros. didn't only give me a familiar Mario experience. It actually helped me see flaws in the earlier Mario titles and appreciate items as not only "power-ups" but as "power-exchanges". It really showed how doing something as simple as having the developers remove flight positively affected the game design and made it feel fresh once again.