I've read where a lot of people started rediscovering Supernatural is season four again because it lost them in season one. My guess would be right about here. It's bad enough Sam's character was all over the map. Now he's relating to a kid who has a little tension with his father? Um, Sam's father was a demon hunter who uprooted his children, taught them how to fight monsters, trained them like warriors, and abandoned them most of the time, thus scarring him for life. This kid and his dad just didn't see eye to eye, you know, like MOST fathers and sons. It was a half assed parallel that made Sam look like a whiny brat. It made Dean look pretty stupid too, for fighting off a swarm of bees with a can of Raid and a lighter is not exactly a "cunning" plan.
You know though, in order to give an episode of any kind an "F", it has to be the kind of episode that happens with a running series that so alienates the viewership that any time they put into the show has been completely invalidated. Considering this was episode 8 of season one, that's not quite the same thing as to what Smallville did to their viewers with that Lana Lang crap in season 8. So, because of that, and one good scene between the brothers while Sam held Indian bones in a box (?), plus Dean's split second win in the steam shower, I bump up that F to a D-.
I actually did a much longer scathing review of "Bugs" a while back. For more detail as to why it is that bad, here's the link.