Okay, now I'm worried. The major, season long villains of Supernatural always had a greater agenda than what they were doing week to week. Whether implied or explicitly stated, the various demons and enemies we've seen through the years had something up their sleeves. This drove the seasons forward as the Winchesters dealt with their internal problems.
This season, however, there's little of that. The Leviathans are formidable enemies, to be sure, but they lack the deviousness of the demons, the long-term planning that leads to great arcs towards the end of the season. While they've proven themselves very capable of causing havoc, the consequences of what they do don't seem to be adding up. Who's to say the Winchesters would be fighting less if the Leviathans weren't around?
The problem with "Slash Fiction" is that it begins with events so shocking the writers had to hit reset at the end of the episode. The Leviathans pose as Sam and Dean and start slaughtering people on camera. This leads to a nationwide manhunt, which puts the brothers in crisis mode. This leads to a sticky situation where the brothers are arrested at the police station. However, the writers decide not to have Sam and Dean chased by police for the whole season, so they create an easy solution involving Bobby's sheriff friend who stumbles upon a way to combat Leviathans with borax. So Sam and Dean are declared dead, the actual brothers escape, and they're fine except for Sam knowing about Dean killing Amy. All too convenient if you ask me.