Gravity's Falls' biggest strength is that it *does* end, and that nothing is held back for a future season. It told the story it wanted to tell and left some mysteries to chew on. Like the twins find out in the final episode, the summer ends.
Alex Hirsch once again shuts down hopes for a ‘Gravity Falls’ continuation: “I’ve been saying, sorry, show’s over for a decade. Yet every single time, someone’s saying, ‘OK, but when are you gonna answer the question?’” (via Polygon)