Supernatural is a drama. The creators consider the show to be a modern western. The good guys ride into town, defeat the bad guys, kiss the damsel, and ride off into the sunset rarely ever seen again. Which is actually how most episodes are formatted. 2 brothers Sam and Dean Winchester are what are known as Hunters. Hunters fight and kill/vanquish anything that is attacking innocents(and sometimes not so innocent). The things they kill range to a large variety of things from Werewolves and Vampires(not sparkly ones, but blood thirsty murderous evil ones), to Demons and Ghosts, and even to Angels and gods. Not God God. No one knows where he is. But gods ranging from Pagan to Egyptian gods. The show incorporates many different cultural beliefs and creatures. They use Native American lore, Pagan Lore, Roman and Greek Lore, and in later seasons a whole lot of Christian Lore. The various evil entities even form different types of sects, covens, and political groups. The Demons have hierarchy, the Werewolves sometimes have packs, and the Vampires have families.
Sam and Dean have an interesting relationship. Their father raised them both to be Hunters. But Sam didn't want that life, and he never really did. The series starts with Sam off at college, and Dean searching for his father who has disappeared. Dean convinces Sam to help him on a hunt, but when its all over and Sam goes back to school his girlfriend is brutally murdered before his eyes in the exact way their mother died. With the feeling of nothing to return to, Sam decides to join Dean and travel the country hunting. The two of them travel back and forth in their trusty stead; the 67 Chevrolet Impala. Unfortunately the Impala has to be completely rebuilt a few times throughout the series. But the true emotional value isn't fully revealed until Season 5. In the trunk are a large variety of weapons, fake IDs and materials which are used for protection, summonings, and concealment.
The show twists and turns throughout the years. Each season generally having a theme or ending goal. For example, Season 2 deals mostly with demons, Season 4 is all about Lucifer and preventing him from being able to escape from Hell. Season 5 is mostly about conflict between brothers. Season 7 is all about Leviathan and their worldwide plans for mass destruction. Even though the season as a whole has these themes or ending goal, not every episode in the season actually has something to do with the end. You could consider these other episodes to be kind of like filler episodes. Or episodes in between all of the seasons main plot points. Essentially showing how the brothers spend their time when they are searching for new leads into how to prevent the catastrophic evil.
Comically the series introduces a Prophet of God whose job as Prophet is to write a new testament of sorts. This new testament that Chuck writes is the story of Sam and Dean Winchester. In other words Chuck writes a book which completely and accurately records the events and actions of Sam and Dean as they fight the forces of evil. Chuck writes these tales and then publishes them under the book series title of Supernatural. Essentially publishing a book for each episode of the series. Supernatural has a small number of fans, of which are all classically nerd obsessed people. Some of these fans even write fan fictions about the characters. Sam and Dean come across these books eventually and the fan fictions as well. Quite a few jokes are mentioned about these fan fictions and how most of them show Sam and Dean as gay lovers. All of this is in reference to real life fan fictions and real life fans of the show. Additionally through the fans a funny little note comes up that Sam and Dean should apparently should keep their weapons on a bungee, because in almost every episode in the show one or both of them get thrown into a tree, or a wall or something, and evidently drop or lose their weapon.
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Everybody Dies. Seriously. Everyone in the show dies. Literally. I have told people this before who are just starting to watch the series and they of course laugh and think i am joking. But I am not. Everybody dies eventually(except Garth...at least not yet) Sam, Dean, their Dad all die and go to Hell. Luckily for Sam and Dean they both are brought back out of Hell. But they did die. They experienced Hell. You meet other Hunters. And all of them(except Garth) die. Some people are brought back, some remain on Earth as Ghosts, but most of them die horrible and often painful deaths. And sadly the fate for almost all Hunters is a trip to Hell after death. Why? Because every Hunter is a Murderer. Most of the creatures they kill were humans at some point. And Hunters eventually all become ruthless and "heartless." They protect innocents, but they kill to do it. While i do love this show, it does start to be a little bit ridiculous when a season ends with Dean going to Hell or Purgatory and a year later gets out. Though Purgatory is explained better than the Hell escape. But it always comes down to Sam and Dean being more important than everyone else.
Another aspect of the show that comes up quite a bit is Psychic powers which Sam gets, but then loses, but gets back. And all kinds of crazy stuff, but luckily that ends eventually. And just so you know the episodes that tend to be the most violent, the most bloody gory are the ones with Witches or Pagan Gods. The Witches curse people so that they die horrible, bloody deaths. In one episode a guy eats a whole bunch of candy. After ingesting it he feels a pain. So he puts his hand in his mouth and pulls out a razor blade. Unfortunately that's not all. The blade is attached to a line, he pulls and pulls eventually pulling out like 3-4 more blades which of course were being pulled out from his stomach and through his throat. Needless to say, he died. The Pagan God episodes are bloody because they all long for sacrifice and worship, need i say more.
I almost forgot to talk about the blood splatter. If you watch the entire series you should note that almost every episode, if not every episode(i currently can't think of a single one that didn't have a blood splatter at some point, but there still might be one) has blood splatter. Someone gets bludgeoned, blood splatter on the wall or floor nearby. A Vampire attacks a victim, blood splatter on the wall behind them. A car drops off a block and traps the mechanic underneath, blood splatter on the floor and wall. And the blood splatter that i will note as the most ridiculous and doesn't make sense for the scenario goes to Episode 16 in Season 7, "Out With The Old." A girl accidentally buys a pare of cursed ballet slippers which make you dance to death. She put them on and dances and dances. Finally at the music crescendo blood splatter all over the walls. Which you find out later that she danced till her feet broke off and she died. I cannot fathom a reason why blood would splatter in that manner on the wall unless she was flicking her stumps repeatedly in the direction of the wall. But i digress.
This show is fantastic. I love the suspense and character development. The fact that they essentially break the 4th wall with fan fiction and random time travel. And a creature known as a trickster doing whatever the fuck he wants to and being mostly invincible while he does it is fascinating. At one point the brothers break through a window only to land on the set the actors are filming on. This throws the brothers characters into our world, and that they are just actors. While it is a "Drama" it has a lot of comical episodes which range from Groundhog's Day Scenarios to being on the Hollywood sets and mentioning the TV Series Gilmore Girls of which has a shared actor. Sam plays the boyfriend on Gilmore Girls whose name funnily enough is Dean.
As I said, I love Supernatural, it is well written. Many episodes are like watching a horror movie, but it 45 minutes. But the show does bring up some ridiculous leaps and bounds, often times leaving gaping hole which you can't help but ask, Really? I give Supernatural a 9.5 out of 11. But as it is still ongoing, and has been planned to officially end after Season 10, we shall see how it fairs in its final moments.