Also, I feel like I might have been the only person in the world to notice at the time, but there are a shit-ton more "fluff" stars in Galaxy 2 compared to 1.
In Galaxy 1, each hub comprised of 2 big levels and several small levels. The big levels usually had 3 courses with unique stars, each one giving you something new to explore within the theme of the galaxy you were in.
Each star also, built upon, and escalated the challenges and mechanics you got into within that galaxy. Each of the main stars in those levels felt like a wonderful ride, and even formed cool narratives through their design. You had 1 or 2 prankster comets on top of that, and maybe a secret star or a minigame. Same deal with the smaller galaxies, with 1 or 2 unique courses and maybe a comet.
With Galaxy 2, each level usually has 2 unique courses and the rest of them are prankster, coin shit, or monke minigames. While the unique courses available are as good (for the most part) as what we got in the first game, there are a lot less of them than you think. Because of that, I feel that Galaxy 2 never made the most of the cool ideas its levels introduced. In fact looking at the list below for Galaxy 2, a few of the levels were 1 main course, then a quicker course and then comet/minigame/secret type stars. Melty Monster comes to mind in particular.
https://www.ign.com/wikis/super-mario-galaxy/Walkthroughhttps://www.ign.com/wikis/super-mario-galaxy-2/WalkthroughCompare the number of unique courses with the number of comet challenges, minigames, etc for each level in both games. Green stars were a cool concept and I'm glad they took the idea further in Odyssey, but IMO Galaxy 1 made way more out of the levels it had.