@Aria I love this show. But I disagree that the show is trash. Most of the plots and storylines are trash - the Leviathans being my least favorite, yes. However, I think the writing is actually better than people give it credit for. It leans into the bad dialogue and overused tropes to reuse things in new and unexpected ways. And, of course, the last 10 or so seasons are very different from the first 2-3.
But where they've really shined is making likable main characters and supporting characters and that's what has kept it around as long as they have. That's why longtime fans of the show are fans. Over time, you grow to love these two brothers whereas if you only sat down for a handful of episodes you'd likely pass on it.
Unfortunately for the producers, it is also the main reason their multiple attempts at spinoffs (3?) have repeatedly failed. People don't love Supernatural as a TV show. They love Sam and Dean (and Cass!). No one wants anything to do with a Supernatural show without Sam and Dean. And in the same vein, if you don't like Sam and Dean (probably because of some undiagnosed mental issue!) you won't like Supernatural.
From all appearances, it is a formula they blundered into - then keenly took advantage of when they recognized that people responded to it in order to last 15 seasons (US network 20~ episode seasons, not these pidly 6-10 newfangled seasons so many shows are doing now). That's no fluke. If you can connect with that thing that they do so well, then you're lucky enough to have 300+ episodes of a fun show to savor. If not, you won't miss much anyway. I, however, will miss it when it is gone. 