While game is filled with some solid gameplay, there's also way too much plain stupid bullshit.

Selecting levels takes way too long due doing it being done via big playable hub area.

Having lives in this game is totally pointless and Galaxy is actively designed around them. You can easily earn a life at the beginning of most levels. Life counter is reset each time you turn off the game and when you do lose all of them its basically just waste of time penalty.

Speaking of wasting time, there's a lot of repeated, unskipable, bland dialog.
Also, to unlock Luigi you need to repeat (quite easy but lengthy) fight with Bowser, then repeat watching boring ending scene and ending credits.

While some of purple coin challenges are one of the best in the game, most of them are far from that. They are long, mostly easy levels, which need to be started from 0 when failed.

Camera is pretty bad. Often it won't let user rotate it, even though doing so would help. Sometimes Mario is straight up not visible behind some objects and when you can rotate it, it's not possible to configurate axis or rotation speed.

Most of levels are really easy and only few provide fun challenge.

Way too many water levels.