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: Super Mario Bros. 2
Broken Base: The third world's dungeon is seen by some as a huge difficulty spike due to the shy guy pots and lots of spark platforms and increased length, while others see it as the easiest dungeon in the game due to the abundance of POW blocks, the near absence of instant death traps, the ease of escaping the Phanto, the fact you get all your hearts early, and the lack of Zerg Rush enemies in the dungeon.
Demonic Spiders: Bob-Ombs, when uprooted, often have an extremely short fuse, damaging you if you don't throw them in time.
Difficulty Spike: Depending on whether or not 3-3 is difficult for you or not, this either happens there or in 4-2, a level with a very hard to find fourth mushroom, Zerg Rush beezos BEFORE you get to the third mushroom, and some annoying platforming involving an autobomb, not to mention fighting Birdo on ice. The difficulty spikes again in 5-3 with an area overflowing with enemies plus a tough climb up inside a tree. Then you have to fight Clawgrip.
Fanon Discontinuity: Some fans refuse to accept the game as a part of the Mario series and refer to the Lost Levels version whenever they bring up Mario 2.
Never Live It Down: The game itself can never live down being a Doki Doki Panic palette swap, with DDP being brought up nearly every time this game is.
That One Boss: Clawgrip... he throws lightning-fast rocks that aren't always guaranteed to slow down enough before going down a pit. Good luck getting past him with Toad or Luigi.
Unwinnable by Insanity: In World 2-2 where you must dig through sand, it's possible to force yourself into a dead end by digging up every sand block until they're out of your jumping range. Since the game has no timer, you're stuck there. Fortunately, the devs accounted for this; see The Dev Team Thinks of Everything on the main page. In fact, this scenario provides the trope's page image.