I watched Supernatural for a while. never got much sense of an overarching plot, a little too isolated episodes'y for me
(but I watched up to the point an angel became god, or something, so...I guess there is one)
I was hoping there would be an episode set in Stars Hollow one day.
The show basically takes the line demons and angels are both douchebags and both ego driven with humanity caught in the crossfire. The majority of angels in the show are worse than the demons and some of the demons are just as likable as the main characters.
As for plot the first 5 seasons? are driven by a single storyline, it gets resolved and then the show becomes more about family in general, and how we don't get to pick those we love the most... or how those we love hurt us the most... or cheese burgers.
In anycase, I love the show. It references itself in a few episodes and there is a running gag about fan fiction in which Sam and Dean are lovers and not brothers. Rare to find a show, even today, that doesn't take the medium too seriously and are willing to break up the format and take chances here and there.
We're not talking the Wire here, or the Shield. But...yeah... I look forward to the show constantly.