It was my childhood series and I can remember myself always begging my parents to but me some merch. Now, I'm 14 and still love the show, rewatched it with my dad a year ago (who, by the way, also liked it very much. At the end of the first episode he was already asking himself why it only had 2 seasons) and noticed so many little details that I couldn't understand or see earlier! Of course, as a kid I also appreciated Alex Hirsch's creation, but now I get that Gravity Falls' storyline is gonna be touching for all groups of ages with its humour and the best written characters with their dynamics. Never going to forget the impression those silly little creatures made on me. 10/10.
I also recommend the 3rd Journal and the Book of Bill, really got me sobbing for God knows which time already because of this universe. They reveal Author's experiences before the chronological start of the show and Bill's perspective on things.