Contains spoilers for Season 15 Episodes 18, 19 and 20
Supernatural is a long show. 15 seasons, to be exact. 15 seasons to develop their characters. Which the writers did, pretty well.
Until they threw it all away in the last episode.
Supernatural is a show about two brothers who hunt monsters and demons, with an overarching plot being included each season. For example, they were looking for their Dad in Season 1 and defeating God in Season 15.
I think that major escalation speaks for itself - the writers had all the time in the world to give Sam and Dean plenty of character development and interesting character arcs throughout the show, which is why the ending of the show is all the more frustrating for viewers.
The beginning of Season 1 saw Sam as having escaped hunting and enrolled in Stanford Law, with a girlfriend and a stable group of friends. He had what is described in the show as an ‘apple pie white picket fence’ life, until Dean crashed it with news of their father’s disappearance. On the other hand, Dean Winchester had been hunting. He expected to die young because that was the life he had chosen - he’d never escaped his father’s expectations like Sam had.
The end of Season 15 saw Dean’s death at only 40 years old, having been killed off by a group of monsters (the episode after defeating God) whilst Sam gets a steady (blurred out) girlfriend and his picket fence lifestyle until he grows old (signalled by way of the actor, Jared Padalecki, wearing a terrible wig).
The ending of Supernatural is circular in the worst way possible, especially when there are multiple instances throughout the series where Dean finally begins to reject the mindset of ‘live fast, die young’ that was ingrained into him by his father, who was determined to take revenge on the demon who killed his wife. It gets to the point where he actually expresses a wish to quit hunting altogether, if not for the apocalypses that occur every season. It shows huge character development, as Dean finally begins to accept that his father pushed them too hard, and he finally begins to see what Sam saw back in Season 1 when he left for university.
Dean’s final death is made worse by the fact that his own ‘apple pie’ life was within reach, only a few episodes ago, in the form of the third recurring character, Castiel. Castiel is an angel, originally tasked to rescue Dean from hell at the beginning of Season 4 before helping him and Sam stop Lucifer from being set free. Over the seasons, it is made clear that Dean and Cas have a ‘profound bond’ (as mentioned in season 6, episode 3) and by season 15, many viewers were convinced that the pair were in love.
They weren’t wrong - in season 15, episode 18 Castiel confesses his love for Dean in what he considered his ‘happiest moment’ before he is killed by an entity known as The Empty - a version of hell for angels and demons. In many ways, his death is a crucial reason for the awful ending of the show. The first is the clear homophobia shown by the writers - Cas is sent to what is jokingly nicknamed ‘super hell’ after his confession to Dean and is then mentioned a grand total of 3 times in the final two episodes despite being a fan-favourite and recurring character since season 4. His death is even worse because Cas has escaped the Empty before. In season 13, with the help of his adopted nephilim child, Cas manages to escape the Empty. The nephilim - Jack - was still alive and well in the last two episodes of the show which begs the question - why didn’t he bring back Cas? Especially in 15x19, when he absorbs all of God’s power and becomes God himself, it hardly makes sense that the first thing he did wasn’t bringing back Cas.
But of course, it comes back to the writers’ homophobia. If they brought Cas back on screen, what would they do about the love confession? It was too far from the planned plotline for them to continue, so instead they have one last mention of Cas in the last episode, saying that he helped to rebuild heaven, before Sam and Dean reunite in Heaven - without Castiel.
It’s frustrating to think that if the writers had been just a little smarter, they could have allowed Dean and Cas to have their happy ending and gone down as one of the first mainstream shows to have such good representation of the LGBTQ+ community. Instead, it goes down in the history books as a failed ending after 12 years of queerbaiting the viewers.
Castiel’s death isn’t the only bad thing about the ending, though. As mentioned, season 15 is primarily about defeating God - with the underlying message of writing your own story, having free will and not letting anyone control you. In the penultimate episode, the Winchesters manage to defeat God with the help of Jack, which is an extremely impressive feat. And then, in the final episode, Dean is killed off by… vampires?
It doesn’t seem right. How can you take on God and then get killed by vampires? Especially when you consider the fact that he didn’t even get bitten - he was impaled on a rebar that was sticking out from a beam of wood. Basically, he was killed by an OSHA violation. There’s even an argument to be made that Dean came back from the dead many times over the 15 seasons (for example when Cas pulls him out of hell) so surely he should have been able to simply come back to life after something ridiculous like this.
An awful ending for Dean - and Cas.
Even the car’s ending (a 1967 Chevy Impala affectionately nicknamed ‘Baby’) is somewhat bittersweet after Dean’s death. This car has been the vehicle during the entire show - maybe the only item that has been consistent over the years. It’s been destroyed and put back together and carried Sam and Dean since they were kids. And in the finale? It’s revealed that Sam put Baby in the corner after Dean’s death. Perhaps it was too difficult for him to drive it - it was primarily Dean’s car, after all, but it’s hardly joyful to see the iconic car gather dust in the garage covered by a sheet until Sam uncovers it when he gets old. If anything, if Sam didn’t want it, it should have gone to another character - perhaps Claire, who was Cas’ vessel’s daughter.
Finally, the worst part is that John Winchester wins. John Winchester, father of Sam and Dean, wins. Dean never escapes him. He tries his best and nearly manages to, but in the end, John Winchester’s insistence on hunting gets the better of Dean, and he’s killed merely an episode after defeating God.
In summary, there are many reasons that Supernatural has the worst ending in TV history, ranging from little details like Sam’s bad wig all the way to the homophobia shown by the writers and the way they killed both Dean and Cas to avoid writing their happy ending. It all adds up and, in the short space of three episodes, it absolutely ruins the ending of an otherwise brilliant show.