My dad heard about it from a friend at work and recommended it to my siblings and me. They started watching it after they finished Phineas and Ferb and they instantly fell in love with it. I was a little hesitant at first, and I actually came in halfway through season 1 (the first episode I saw was "Bottomless Pit!"), but when I saw and heard Dipper I thought, "Wait, that kid acts a lot like me. What is this show?" So I gave the show a chance and immediately fell head over heels for it.
(My first experience with Dipper was when I heard his line, "Grunkle Stan, do I really have to be the one to point out that a bottomless pit is- by definition- impossible?". I've always kinda been that one really rational person in my social life, and I thought that that line sounded like something I would say, so I continued watching to see what else Dipper would do. Thank you Alex for giving us such an awesome show!)