I'm in World 6 now with 76 Stars. I'd actually have a lot more by now, but when I saw in World 5 I had enough to get to Bowser Jr. pretty much right after the first galaxy, I took the opportunity to get him out of the way (unfortunately, I missed the Comet Coin there so I'll have to go back anyway). Now I'm just working my way back through the World 5 galaxies to get those knocked out along with their comets (so far I've gotten all the stars and comet stars in the previous 4 worlds except the final Bowser comet in World 4). By far the worst stars I've had to deal with so far are the ones that involve the Shadow Marios, particularly the one in Chainchomp Factory. And oh joy, the Spring Suit returned in that stage, because it worked
so well in the first Galaxy and was beloved by all.

I also had a lot of trouble with the Purple coin challenge on the tile-flipping galaxy in World 1, though in my defense part of that is because the stupid waggle-activated spin attack would only work about 3/4 of the time. Frequently running through that stage, I'd shake the remote and
nothing would happen, causing me to fall through the un-flipped tile and die. Ugh, I hate waggle. Why couldn't this just be done with a button (or at least have the option), like the B trigger? It's not like there's much point to the stupid pointer-based Star Bits gun besides (occasionally) triggering coins during boss battles.
And there's a Mario Sunshine galaxy! Damn it, I thought we threw that crappy game back into the fires of Mt. Doom from whence it came!

I'm actually kind of surprised they didn't bring FLUDD back for that stage.