These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Awesome Music: The first show in the franchise to feature an original theme tune rather than a remix of the original. The result is epic!
Dude, Not Funny!: A literal and decidedly unhumorous version when Brooks and Devlin interrogate a man about the murder of a boy who lived in his apartment building. The man had been the prime suspect 20-something years earlier when the boy disappeared and is clearly still bitter about the bigotry and homophobia he dealt with. As such, he sarcastically confesses (NOT an example of said trope) to having killed the child, to which a thoroughly unamused Matt replies, "That's not funny, Mr. Connor."
The man's black sense of humor returns in a more satisfying way when the real killer confesses in court and the original suspect gives him a harsh and heartfelt Slow Clap.
Fanon Discontinuity/He's Just Hiding: Most fans reaction to anything after "Deal". The number of fanfics in which Matt recovers from his wounds and marries Alesha vastly outnumbers those that focus on the aftermath of his death.
"Funny Aneurysm" Moment: DI Chandler comments to Ronnie and Matt that whoever cleaned a crime scene "must be a fan of CSI". Shortly after leaving the show, Jamie Bamber, who played Matt, guest-starred on an episode of CSI: Miami. Even "funnier", after several years of playing a by-the-book cop, he was now playing a criminal. . .named Ronnie.
In the episode "Samaritan", not only are they investigating the shooting death of another police officer, Matt muses to Ronnie that it must be tough to lose a partner, then fumbles as he realizes that he's just reminded Ronnie of his previous experience. Then, in the episode "Confession"—which is also centered around the shooting death of an officer—Ronnie tells the man's grieving partner, "God forbid Matty here got himself shot, I'd be out there straight away trying to find out who did it and string him up myself."
A year later, that's precisely what happened, making both situations and statements an eerie, inadvertent Foreshadowing. The irony becomes even crueler when you recall that throughout the show, it was Matt who would flip out if/when Ronnie seemed to be in danger.
And an "out-show" example: Matt was killed by someone seeking revenge against the police for bungling the investigation into his brother's murder—something he had nothing to do with. The recent murders of two NYPD officers by a man who wanted to avenge the death of Eric Garner (a man suffocated by the cops as they attempted to restrain and arrest him for selling loose cigarettes. The officer who applied the fatal chokehold was not indicted) bears an eerie similarity, right down to the fact that the officers in question had nothing to do with the aforementioned incident and that their killer was intentionally targeting the police.
Hollywood Pudgy: Brooks is at worst moderately overweight, yet teased as though he's morbidly obese.
Replacement Scrappy: Sam, both out and in-universe. He wasn't a bad guy, he just wasn't Matt. Some of his less-than-stellar moves—sarcastically pretending to be racist, sleeping with a victim who turns out to be the killer they're after, rebuffing Ronnie's efforts at mentoring and friendship—didn't do him any favors either. It's telling that he only lasted 2 series and disappeared without any explanation.
Kate as well. Her very first appearance was as the defense attorney responsible for killing 15 people by causing a train crash, she answers Jake's cell phone without his permission, then proceeds to relentlessly butt into his personal life by badgering him about going to his mother's funeral, and she foolishly—and perhaps deliberately—tips a defense lawyer off to the tactics that Jake intends to use.
Seasonal Rot: Starting with Series 5, following the departures of Ben Daniels and Bill Patterson, kicking into high gear in Series 6 with Jamie Bamber's defection before maxing out in Series 7 with only one original cast member remaining. Their replacements, while not bad actors or characters in their own right, simply did not have the flawless chemistry of the original cast—in particular, Ronnie and Sam never had the rapport that Ronnie and Matt did. As such, the episodes, while still very good overall—"Deal/"Survivor's Guilt" are unanimously considered among the best—were not as good as those from the first several series.
Spoiled by the Format: For fans of The Mothership, once you see which episode forms the basis for the UK episode, who did what and why, as well as what will happen is fairly apparent from the start. Especially bad with the "Survivor's Guilt": Once you know it's based on "Suicide Box", you know Matt wasn't shot in retaliation for a drug dealer's conviction. That said, the UK writers tend to change things enough to keep it interesting, and most episodes aired so long ago, it's virtually impossible to remember every plot twist that took place.
Stoic Woobie: Alesha. When Matt tries to comfort her following her rape, she simply hands him a videotape of her assault and asks that he arrest her attacker. Later, she manages to keep it together during the investigation into Matt's death and the prosecution of his killer, and in the episode "Line Up", she conducts a virtually flawless prosecution of a young girl's gang rape. Although she's clearly motivated by her own experience, she shows no signs of letting it adversely affect her.
Matt himself could count. In several episodes—"Alesha", "Confession"—despite clearly being deeply personally affected by the circumstances of the cases—his friend raped, another has committed suicide—he does his best to put his feelings aside in order to support those involved and see that those responsible are brought to justice.
Ronnie as well. There are numerous scenes in "Survivor's Guilt" and "Hard Stop" where he's clearly just an inch away from breaking down, but without fail, every time, he pulls himself back together—to the point where at the end of the latter episode, he actually buys a bottle of vodka before walking out of the store without it—and redoubles his efforts to make sure Matt's and Wes's murderers are caught and duly punished.
And Natalie, who waits until she's alone in her office with the blinds drawn to cry over Matt's death, and refuses to break down during "Pride", despite the overwhelming evidence that her father is a killer.
What an Idiot: Yes, Sam, sleeping with the "victim" was a brilliant move.