I sort of see Galaxy 2 as an extension of Galaxy 1 in a similar way to the Star Road section of Super Mario World - those levels are my favourites of the game. While they are separate from the rest of the game, the rest of the game still exists — Star Road is not satisfying outside of the existence of Mario World. My favourite 3D platforming is from Galaxy 2, but Galaxy 1 is where the magic of the universe and the unparalleled story/atmospheric experience is. Combined, SMG1+2 is the best of both worlds.
So even though I do like the levels of 2 mostly better than 1, the experience is significantly less without the experience of 1. If you can only play one of the two, make it Galaxy 1.
If Nintendo makes a Galaxy 3 I really hope they capture everything in one game.
I describe myself as a little dose of toxic masculinity.