I recently acquired Supernatural based on a few positive mentions here on KIA2. I quite like it, but it's a bit... off. These sorts of shows are really about the banter and camaraderie, with the monster stuff being almost incidental. Somehow the chemistry/banter is not quite working for me.
Should I persevere?
Indeed. There is maybe a brief rough patch after season 5, since the show's creator was off doing other things at the time, and he'd mostly planned out the overarching plot for those 5 seasons.
Definitely picks itself back up after that brief slump though. Can't quite recall how long the slump lasted. Somewhere between 1-3 seasons if I'm remembering right. The Leviathon stuff was sort of the final climax of those rougher seasons.
After looking stuff up to refresh my memory, I'm almost positive it's around season 8 that it got things going proper again.