It's actually my least favourite episodes and it's not for the reason most people hate it.
Watching Family Guy is supposed to be a light show. It's not always funny and some of it I think is "meh". That episode was intense, serious and very dark. I watch enough dramas, horror, thrillers and crime documentaries, but Family Guy is a sitcom and should stay being what it is.
I'm not a big Family Guy fan, I find the Simpsons much better, but I still enjoy watching it. I just don't like it when they try to do a drama episode. If I want drama, I'll watch Criminal Minds, I really love that show.