Alternative Character Interpretation: Morland Holmes seems deliberately written to invite this, as his motives and sincerity are always put into question and even to the very end viewers are left guessing about just how good or bad he is.
Anti-Climax Boss: Moriarty. After being built for half a season, her capture in the Season One finale was this for some. Worth noting, however, the original "Napoleon of crime" only appeared in one Doyle-written story (and died at the end of it), so it's actually more faithful to the original work to have Moriarty ultimately be a relatively minor Arc Villain instead of the series' Big Bad, although this version remains an occasionally Recurring Character whose history with Sherlock and international crime organization would continue to have impact on the plot.
Ass Pull: In "The Marchioness", the revelation that Joan slept with Mycroft during the events of "Step Nine" makes absolutely no sense within the narrative and pissed off the majority of the fanbase.
Award Snub: In six seasons, the show never won a single Emmy award and its only nominations were for the main title and credits, not the writing, acting or directing.
Badass Decay: Sherlock spends the first season getting excellent character development and humanization thanks to his improving friendships while also speeding through cases. He spends the second season arguing with Joan, getting upset and anxious over the thought of Joan leaving him, getting jealous about Joan's relationship with Mycroft, and possibly turning back to drugs once Joan moves out. Thankfully, he rebounds in the third season after some time apart from Joan.
Base-Breaking Character: In the second season, Mycroft. Some fans found him to be a strong character and loyal to the canon, while others found his plotline tedious and overlong and his relationship with Joan a complete Ass Pull.
Broken Base: Was the second season finale brilliant or awful? Was the second season in general as good as its predecessor or an uneven, heavily flawed season? Most fans seem to lean towards the latter, especially with the implication that Mycroft pulled a Reichenbach fall and not Sherlock by faking his death to save the day, despite RF being a pivotal point in Sherlock's character. Not to mention that Joan's making plans to move out of the brownstone, stating that she needed to grow away from Sherlock despite essentially one-upping him all season. And then Sherlock is seen with drugs he'd stolen from an earlier episode, contemplating using again!.
"Child Predator": Adam Kemper is The Man Behind the Man to Samuel Abbott. When Abbott kidnapped Kemper, Kemper was able to bend Abbott to his will, even forcing him to live in squalor. Kemper forces Abbott to kidnap and murder five children. When Kemper is arrested, he pretends to be a innocent victim with Stockholm Syndrome, and is offered an immunity deal. After Abbott is confronted and commits suicide, Sherlock realizes he's been had. Kemper brags that he will escape prosecution, until Sherlock notices a loophole in the deal, and confronts him while he observes future victims on the playground.
"One Way to Get Off": Wade Crewes murders couples by tying them to chairs and executing them with a bullet to the head. Crewes would gloat to the cops when questioned, until Gregson's partner planted his prints on the scene. Years later, his secret illegitimate son, Sean Figueroa, reaches out to him. Crewes convinces Figueroa to continue his crime spree, killing another two couples as well as a guest, and attempts to frame a man with the gun and cigarette butts. When Figueroa confesses the crimes, Crewes is confronted with the evidence, but still insists that he is innocent and denies having a son.
"The Illustrious Client" & "The One Who Got Away": Adelbert "Del" Gruner uses his corporate executive status and charming facade to attract many women, before kidnapping them, and torturing them with his branding iron, while also raping them. This kind of brutality would last for weeks before his victims would succumb to their wounds, while Gruner would find more women, having doing this for years racking a body count in the dozens; Kitty Winter was the only survivor of Gruner's cruelty. When Gruner learns that Kitty is trying to bring him to justice, he tries to incriminate her, while continuing his killing spree in New York.
"Scrambled" & "Hurt Me, Hurt You": Tyus Wilcox is introduced as the seemingly-innocent brother of Bonzi Folsom, the leader of the South Bronx Killers gang. He is later revealed to be secretly running the gang, and has Folsom killed with bleach laced cocaine when Folsom receives too much police scrutiny. In the next episode, Wilcox kidnaps Carmen, the innocent sister of Mara Tres gang leader Halcon, forces her to read out a message on camera, kills her, and sends her body along with a recording of the video to her brother. Halcon, in retaliation, has a SBK party massacred, killing ten people including two children. Wilcox, knowing that the police would want to prevent the war, sells out his entire gang to receive a full immunity deal. Wilcox then calls Joan Watson, mocking her over the death of gang informant Shinwell Johnson, and scoffing at the idea of being loyal to his gang.
Alfredo and Bell have their fair share of admirers.
Clyde the tortoise is also rather popular as well.
There's also clamoring for seeing more of another character: the crusty snow-plow driver, Pam.
Despite only appearing in a few episodes in the early seasons, Ms Hudson is extremely popular among fans due to being a very positive and respectful portrayal of a transgender character in a mainstream show and one who is played by a transgender actress as well. Her appearances are always well-received and many wished she would've gotten more episodes.
Fandom Rivalry: Fights with some factions of the Sherlock fandom have gotten to the point they've reached national newspapers. A big point of contention was over whether Jonny Lee Miller or Benedict Cumberbatch was the superior Sherlock, conveniently side-stepping around the fact that the actors are good friends and colleagues in real life. Tensions have calmed only at the second series, where even antagonistic fans admit that Elementary isn't that bad. They've also calmed after the divisive fourth season of BBC's Sherlock turned many fans against the show.
Between Moriarty and Joan, especially during the restaurant scene. Also, the traditional Holmes-Moriarty Foe Yay is given a new dimension by having Moriarty be a woman and having her and Holmes actually having been lovers once. Later on, we learn that Moriarty now considers Joan a Worthy Opponent, just like she does with Holmes.
In "The Female of the Species," Moriarty arranges for the murder of a criminal who was targeting Watson because as far as she's concerned, Holmes and Watson belong to her and her alone.
"Miss Taken" ends with the unnamed conwoman taunt-flirting with Holmes and saying she hopes he'll be at her trial. She also seems quite visibly pleased to see him visit her in her cell.
Seems to be striking up a relationship with Sleepy Hollow, as they both have female characters of color who take no shit. It also helps that the Twitter pages for both shows' writers have been engaging in a hilarious Twitter "feud", with the CSI writers piping in.
"Solve For X" revolves around "P versus NP," the most notorious unsolved problem in theoretical computer science.
In "An Unnatural Arrangement," we meet a character with the unfortunate name of "James Monroe," and British Sherlock Holmes quips "Loved your doctrine." Britain was one of the only European nations to actually be in favor of the Monroe Doctrine.
It Was His Sled: Irene really being Moriarty quickly became one of the most well-known things about the series.
Like You Would Really Do It: The series finale has a fake-out where it tries to imply that Joan died of cancer by cutting from her and Sherlock after the news broke to a funeral, where Sherlock talks about the unnamed woman who died. Given the entire basis of the series is their relationship, the idea that they'd kill her off in the finale was was incredibly unlikely. It turns out that the funeral is for Moriarty.
Magnificent Bitch: Jamie Moriarty is a criminal mastermind who has orchestrated many assassinations. When Sherlock Holmes interferes with Moriarty's plans, she cultivates the identity of Irene Adler, and manipulates Sherlock into falling in love with her before faking her death driving Holmes into despair. She would also set her "killer" Sebastian Moran, up as a Serial Killer and later has Moran kill himself before he reveals anything about her to Sherlock. Revealing her true identity to Sherlock, she arranges the Greek business man "Narwal" to kill a Macedonian diplomat, leading to Macedonia not joining the European Union and switch to the Euro currency to which Moriarty would make billions out of their current currency; Moriarty would have gotten away with it if wasn't for the sudden intervention of Joan Watson. Now confined in a highly secured prison she helps Sherlock and Watson find her subordinates before escaping her confinements and kill them herself when they kidnapped her daughter before going back to prison. She also has her daughter's father be her successor to her criminal organization, and later allows Sherlock's father Morland take over, before escaping her prison and waiting for Morland to die before reclaiming it. Faking her death several times to elude authorities and have Sherlock and Watson arrest all her rivals, Jamie Moriarty ends the series with her deviousness and brilliance only matched by the detective duo's determination to bring her to justice.
The pilot has Dallas Roberts play the role of the psychiatrist who manipulated the killer of the episode into murder. Roberts played recurring characters in The L Word, Rubicon and The Good Wife prior to this role. For many viewers watching the show after the initial airings, Roberts was obvious as part of the conspiracy because his next role after filming the pilot was a very important role as Milton Marnet in The Walking Dead.
In "Lesser Evils", the seemingly tiny role of the janitor was played by David Costabile, aka the Big Bad on Suits aka Gale Boetticher, a major role in Breaking Bad. A character who turns out to be an additional killer also falls under this, as he's played by David Harbour, of The Newsroom.
In "The Long Fuse", Lisa Edelstein (Dr. Cuddy on House) plays a business executive who turns out to be the bomber.
"Deja Vu All Over Again": Subverted. The show features Jim True-Frost and Andre Royo, both of whom will be very familiar to viewers of The Wire. Neither one did it.
"Snow Angels": We see the female murderer at the beginning, and she is shot by her victim right before he dies, but don't get a very good look at her because of a disguise. Later in the episode, we meet a girl played by Jill Flint of Royal Pains, who claims to be a stab victim, but who Bell takes in as a suspect. And yes, she did it.
"Blood Is Thicker": The wife of Gale the internet billionaire is the killer. She is played by Margaret Colin who recently finished a 5 year stint as Eleanor Waldorf on Gossip Girl.
"No Lack of Void" features Garret Dillahunt (AKA Cromartie and Burt) as the killer of the episode.
The killer in "Dead Man's Tale" was Patrick Fabian, who was a deep-sea salvage expert who was trying to pull off a The Producers style plot where he needed to fail rather than succeed. Fabian has had major roles on shows like Gossip Girl and more recently, Better Call Saul.
Paranoia Fuel: The idea that your beloved significant other is not only a career criminal, but a career criminal that is hellbent on destroying you. So much so that they invented a whole persona for you to fall in love with, just so they could get close to you.
Periphery Demographic: In addition to Holmes fans and fans of the police procedural, Elementary has gained an enthusiastic following from progressives, especially feminists, not just for Gender Flipping Watson and Moriarty, but also for subtle signs scattered throughout the series that the show's makers are earnestly trying to make the show progressive and pro-feminist. Judging by the enthusiastic response, they've largely succeeded. It's also praised for being one of the few shows with an Asian lead character.
The Producer Thinks of Everything: The show's first season was acclaimed by the fandom due to the several continuity nods (from the "Pilot" to "Heroine", the season finale), consistent Call Backs, details scattered around the episodes, good Foreshadowing, a significant soundtrack, and a solid story arc which developed in a right pace.
Seasonal Rot: Many fans point to Season 5 as the weakest when it comes to the seasonal Story Arc, as it revolved around an Unintentionally Unsympathetic character (Shinwell Johnson), a forced conflict emerging between Sherlock and Joan, a lack of personal stakes, and ending on the Shocking Swerve of Sherlock developing brain damage for the sake of setting up the next season.
Ship Sinking: The Kitty/Sherlock ship goes down in flames when she returns to New York in a two-parter and is revealed to have a child, among other changes in her life.
The third season finale. Sherlock finally relapses into drug use for real, and now his perpetually unseen father is finally coming to New York City to face his son in person.
Sophomore Slump: The second season was as enjoyable the first as far as episodic plots are involved, but was marred by Conflict Ball-induced stupidity, Sherlock and Joan bickering rather than getting closer like fans wanted, and Mycroft's drawn-out plotline, and a somewhat unbelievable romantic subplot with Joan. Season 3, thanks to Kitty's terrific character arc and a saner dynamic between Joan and Sherlock, was a return to form.
Tough Act to Follow: Each season tends to end on a slew of continuous episodes that close out the season's Story Arc. General consensus seems to be that regardless of how good or bad they are, none have topped the ones from Season 1, which centered around the iconic adversarial relationship between Sherlock and Moriarty.
Abigail Spencer takes the cake for having one of the most tragic stories in the entire series. Her backstory with Sherlock also makes you feel bad for the kind of childhood they both had.
And then there's Kitty Winter, who was held hostage by a serial rapist/killer, an experience that left her physically and emotionally scarred. Thanks to the friendship of Holmes and (eventually) Watson, she not only starts to heal, but finds the man who victimized her... and decides not to kill him (although she gets her revenge in a rather horrific way).
Sherlock is one himself, with his past, and his constant struggle with addiction. He's technically a victim of, at least, emotional abuse from Moriarty. And he's got some pretty potent puppy dog eyes.