I haven't watched much Gravity Falls (will in the future, just not at the moment) but something people have said re: Star Vs. and it is what I kind of agree with.
Mainly that GH was super obvious from Day 1 with DEEPEST LORE and SECRET CLUES and shit, while if you just watched the first Star episode you'd be justified in thinking it never progresses or changes and is more of a typical lolwacky cartoon comedy that would've been more at home in the last decade. And so while people who expected mystery 'n' shit from GF obviously got it, people only found about the whole lore/mythology/etc. of Star if they gave it a chance and stuck with it for a bit. Same thing as Steven Universe I guess, but since SU came out first it also was compared favorably to Star because it had more episodes to prove itself.
Now I think Star finally does have a reputation for having the leep dore among people who don't watch it, but it was a long time getting there and overcoming its reputation as plotless/lolrandom. I still regularly see people starting it who say "I know not to expect much plot..." and so on.
I really like the way Star Vs. has built on things but people aren't going to get the impression it does that unless someone tells them or they watch it themselves, and if the first episodes don't grab you (understandable) you can come away with a view of its progression, plot etc. that is wrong just from being based on a lack of information.