My only complaints are almost entirely down to presentation. The faceship feels less like a hubworld and more like a level select menu, because that's almost exactly what it is. The script is somehow even more underwhelming than its predecessor, as if all of the soul was sucked out. It reeks of being purposely bland in order to remain marketably safe. It also immediately weirded me out as a kid how the characters were seemingly acting as if Galaxy 1 had never happened.
On the technical side, oh boy nintendo sure does love wasting cumulative hours of their players time with unskippable bullshit text and cutscenes that you've already seen earlier in the game. I had only 15 more stars to collect after beating bowser the first time. Was the credits sequence skippable the second time round? No, no it was not. Luigi repeating himself verbatim and boss cutscenes only being skippable for already collected Stars but not comet stars are the real bugbears though.

Anyway the actual game is great. Yes, it's so similar that my memories of the Galaxy duology turned out to be a jumbled mess upon revisiting both, but more levels and new traversal powerups is all the formula needed in the first place in order to provide a valuable experience.
10/10 kids game, that's sadly too easy to excite my jaded gamer brain anymore. I'll probably play it again in a half-decade anyway though.