Anti-Climax Boss: Pretty much every main boss can become this, considering you can just stunlock them. However, even if you fight them the fair way, 2 manage to be anti-climactic anyway.
Morton is a big offender, especially after being a contender for That One Boss in Wii. Here, all he does is stand practically glued to the floor and spam easy-to-dodge spiked ball attacks. Oh, and he takes a really long time to generate the spiked balls, too.
Bowser is one of the biggest examples in the entire series. The first phase is a generic fight involving Boss Arena Idiocy. The second phase basically boils down to dodging his slow-ass claws for about 2 minutes while occasionally stopping to jump over his fire breath. It's especially a let-down when it's sandwiched between his innovative fight in Wii and his awesome fight in U. And then the True Final Boss, Dry Bowser, has basically the exact same fight.
This is the first Nintendo game to feature paid Downloadable Content. Whether this is a sign of Nintendo's modernization or its descent into greedy corporate hell is still hotly debated. Is the coin rush mode itself is a good addition for the game, or is it just a half-assed work to grab money from the fans for extra levels?
The excessive quantity of coins is one of the most heated topics in the discussions around the internet. You will never see the game over screen, since it's pretty easy to earn multiple lives in a level. Some fans think it's understandable since the coins are the main theme of the game, but others think this breaks the game, making it too easy.
Contested Sequel: The game's reuse of assets from New Super Mario Bros. Wii, such as the graphics, music, and engine, has been a major point of contention. Some fans don't mind and still think it's a solid game, where others have been angered and have accused Nintendo of getting less creative in its Mario titles. Still others fall somewhere in the middle.
The Invincibility Leaf. If you die five times in a level, this item shows up in the beginning of the stage. Like the name says, you can't die (except if you fall in a pit or in a lava pool) and you have a full P-Meter, so you can fly all over the level.
It's Easy, so It Sucks: One of the most heavily criticized aspects of this game was the lack of challenge. Getting to Bowser is pretty much a cakewalk. The game doesn't get noticeably difficult until you get to the bonus worlds, and even those are not as brutal as we've come to expect from this series.
Nightmare Fuel: There is nothing okay about the giant Boo (Boohemoth) that follows you through most of the Ghost House in World 2. It's huge, it has a terrifying face, it doesn't follow typical Boo rules (it will inch forward even if you look directly at it), and if you touch it? Instant death.
That One Level: A few of the warp cannon levels can be nightmares, especially World Flower-Cannon.