Taking a wrong turn is not a unique idea. A couple murdering "innocents" or butchering them, it was a bit unique for 1980. It all has to do with how the two leads- the couple owning the motel- have gotten into their parts. They are not entirely convincing, and that is what makes them special. Real serial killers are sociopaths 99% of the time. They can communicate well, they laugh at times. Cold-blooded in a way, that was never presented up to this point in cinema history. With the exception of Deranged about the life of Ed Gein, this was a fresh approach, that still holds up.

It can't make it to the top of any list, but this belongs here. Keeping bodies in the backyard! It is a true nightmare. The owners trick you to think they are just an old couple. The movie tricks you into believing this is a comedy of sorts. And then it hits you at a deeper subconscious level. This is a Gacy-Dahmer case, this is possible, turning people into vegetable-meat-zombies. Not for fucking them, like those two did, for treating them like livestock. Imagine a world without animals. The demand for meat will force some people to find their way of creating their own little human farms. It is a scary thought!