My sister watches it but she also enjoys Once Upon A Time which I think ruins her credibility.
First off, that's kind of hilarious.
Second, I have not watched it, but I know a lot of people who rave about it, and have told me I ought to watch it. I make a rule of pretty much never watching anything anyone recommends (joking, but it's turned out that way for the most part regardless), but enough people have said it that I think it's probably at least worth checking out.
Watch up until the end of the first encounter with Jeffrey Dean Morgan. There's a huge part after that that is required, but afterwards it becomes a Revelation splattered hogwash of a show. And I'm a huge fan of the Winchester brothers, for crying out loud!