These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: New Super Mario Bros. 1
Angst? What Angst?: Mario (or Luigi) certainly doesn't have any qualms seeing Bowser get Stripped to the Bone after the first boss battle; they just say their end-of-boss phrase cheerfully and move on.
Anti-Climax Boss: Bringing a Mega Mushroom to any boss will squash them in a single hit. Even the final boss can be defeated in two stomps!
Fridge Logic: Why does Bowser Jr keep screwing time waiting for Mario to beat each world boss to drag Peach to the next world when he could just run all the way to the last castle without wasting time?
Game Breaker: Against bosses, the Mega Mushroom will destroy ANYTHING. Even Bowser.
Power-Up Letdown: The Mega Mushroom looks awesome, but if you break a pipe, you can't go down it, ruining your chances of potentially finding a Star Coin. Also, the Blue Shell handles awkwardly with its sliding mechanic, though it does improve your swimming. The Mini Mushroom, meanwhile, lets you jump higher and with (much) floatier physics, as well as access certain areas otherwise inaccessible, with the drawback that it has zero hit points; one hit from anything will kill you. When you're going for all the Star Coins and have to use it in the later levels where things get hectic...all those lives you accumulated in the early levels are going to come in handy.