Mystic Falls High School inevitably became a battleground for supernatural species in The Vampire Diaries, and several showdowns took place within the school premises. Fans couldn't help but wonder why the school authorities didn't take a step to tighten up their security, especially since the town council knew that vampires existed.
Deaths like Vicki's and Sarah's were just brushed under the rug. Typically, even a single student death would create a furor in an educational institution, but Mystic Falls High School was conveniently devoid of any real authority figures.
Vampires could compel humans to do as they pleased, but how compulsion worked and wore off was a mystery on TVD. For most characters like Damon, Elena and Alaric, their compulsions remained intact when they reverted to human form, but in Stefan's case, every person he compelled started remembering the moment Bonnie gave him the cure in Season 8, which led to his arrest.
This was a big retcon in the show and only delegitimized earlier plots where compulsion had stayed intact.
Damon Salvatore's behavior and characterization in the early seasons of The Vampire Diaries made him a problematic romantic lead, especially as the one Elena ended up with. He dated and slept with Isobel, her mother, and he had also been controlling and abusive to Caroline, who was her best friend.
The show ignored all of his evil deeds at the beginning of the show, making Elena choose him over Stefan. Elena cared deeply for her friends and family, and it was very out of character for her to marry the man who tormented them in the past. This was why this teen show couple made fans cringe.
The Vampire Diaries was full of heartbreaking deaths and even the most powerful Originals and vampires weren't immune.
Matt's neck was snapped, he drowned, got stabbed and his heart stopped, but nothing kept him down for too long. It was absurd that the only human managed to cheat death and even killed other vampires and as well as an Original successfully.
The Vampire Diaries was not known for diversity, and what made it worse was that the only main character of color often got subjected to the worst plot lines. Bonnie Bennett was killed numerous times and was given an inexplicable savior complex that only transformed her into a plot device. She was meant to be a key player, but the show consistently mistreated her, pushing forward a horribly racist message off-screen.
Bonnie's character needs were dismissed in light of what Elena, Stefan or Damon wanted her to do to rescue them. Her powers only existed to be at their disposal, and there were entire episodes where she was forgotten.
The Doppelganger plot was one of the strongest stories in The Vampire Diaries, but the writers constantly retconned the origins of the magical twins. At first, Esther's creation of the Originals led to the creation of doppelgängers, who served to control Klaus' hybrid side. With the advent of Silas, Qetsiyah, and Amara's love triangle, the writers changed the origin story.
Stefan and Elena were both doppelgängers of Silas and Amara, and they existed because nature wanted to balance Silas and Amara's unnaturally long, immortal lives. The first origin story was actually very interesting, but the second one just seemed to drag. It also nullified all the lore that the show had worked hard to establish in earlier seasons.
Few characters died permanently in The Vampire Diaries. In fact, it became a predictable plot twist for important players to perish in some way and then return in the next season.
It lowered the stakes and made the show much more predictable to viewers. This was a kind of safety net that made the show boring and decreased audience anticipation. The plot armor that the main characters had was immense and irritating.
In the first few episodes of Season 1, Damon Salvatore had several mystical powers besides being an immortal vampire.
However, these powers mysteriously vanished as the show went on, never to be mentioned again. It was odd to showcase these abilities in the initial episodes and then just forget about them when it was convenient. Yet another continuity error in a character arc made it hard to take the show seriously.
There was never a good measure for how powerful every vampire was in The Vampire Diaries, even though canonically, an older vampire was much mightier than a fledgling, with the Originals being the strongest. Still, there were enough times when Damon and Stefan overpowered Elijah and Klaus, who had thousands of years on them.
It made no sense that they even stood a chance against, let alone beat an Original vampire. In the spin-off The Originals, Klaus and Elijah were able to take on entire armies of vampires.
When Nina Dobrev exited the show, Elena was put under a magical coma in-universe by Kai. There was no way to reverse this magical spell that was tied to Bonnie's life, which meant that Elena could only wake up when Bonnie died. Conveniently, this magical spell was lifted in a span of minutes in the finale so Elena could reunite with Damon, even though Bonnie was still alive.
This might have been more believable if the writers had provided some sort of explanation as to how the curse was removed. When a magical spell takes a character out of commission for two full seasons, its reversal needs to have some grounding in the show's lore and logic. If Dobrev could only return for a single episode, there were ways to show the progression of this arc before its completion.
