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.
Adult Fear: Quite a bit. The finale comes to mind, wherein a K-12 school is blown up, killing every child inside. Other episodes involve dying children, lost children, or abused children, among other examples.
Deader Than Disco: This was a Top 10 show at the height of its run, even outdrawing The Simpsons in its Sunday night time slot, but after a schedule switch to Saturdays, the ratings plummeted, and many former fans now pretend it never existed. Or that they only watched ironically.
Monica's crisis of faith and temptation by Satan in "Netherlands" is the direct result of her witnessing a building being destroyed by a bomb, killing many. It aired May 6, 2001, and a repeat had to be pulled from CBS's schedule in the wake of 9/11 later that year.
John Dye, who played Andrew — an angel of death — from the second season onward, died in January 2011 of a heart attack. Out of the four main protagonists, he was the first and (thus far) only to go.note And, ironically enough, the youngest cast member of the quartet.
The first season of the show had an angel of death named Adam as a recurring character. He was played by Charles Rocket, who committed suicide in 2005.
Season 3 had an episode "Sins of the Father," where a character played by Robert Ri'Chard has, and takes, the chance to walk away from gang life after being tempted to kill a man. Four seasons later, Ri'Chard would star in an episode where his character kills a former mentor and is sent to prison for at least 25 years.
Innocent Bigot: As mentioned on the main page, Gloria was this for part of an episode. A couple of episodes also imply that Monica has been this toward blacks and homeless people, simply because she had never been either and thus did not fully understand them. Each episode where this trope is used has Monica undergoing an epiphany so that she is no longer the Innocent Bigot toward that group, but Unfortunate Implications still exist.
Mama Bear: Tess can behave this way to anybody who tries to hurt Monica (see "Clipped Wings" for a particularly good example). She's like this with Andrew too, but much more so with Monica. Monica herself can be this way to people or demons who try to hurt assignments, especially children.
Nightmare Fuel: A surprising amount of it. "The Man Upstairs", "Into the Light", and "The Occupant" come to mind.
Gregory, just Gregory. Unlike the shows fairly tame portrayal of Satan he was like a demon from a horror movie complete with demonic growls as he was exorcised.
"Redeeming Love" from season four has some of this. The episode involves Monica helping a crack addict named Lydia, and viewers are spared nothing when it comes to the withdrawal process. In-universe, Lydia has some nightmares of her own, one involving a giant spider.
Any episode involving explosions, guns, or other violence can be this depending on the seriousness of the situation. The same is true for episodes involving mass or graphic death. Season two's "Dear God," involving the Holocaust, and season four's "The Spirit of Liberty Moon," involving the persecution of Chinese dissidents, get special mention.
Oireland: Depending on how you feel about her accent, Monica is this. Kevin Greeley nods at this trope when he mocks her accent, as do Kathleen and Monique (made odd on Kathleen's part because her name actually is Irish). The episode "Life Before Death" could be considered this.
A serious case of YMMV, but there are some. For example, in "An Angel by any Other Name," Carolyn, a woman determined to close a group home for individuals with Down Syndrome suffers a stroke that gives her impaired mobility and speech. The implication being that God reserves the right to punish people with Laser-Guided Karma. There's also the implication that disabled individuals are permanent children; Tess refers to the group home residents as Andrew's "kids" even though they are all young adults. Two are even married. Other implications may be:
Good people always go to Heaven; "bad" people always go to hell
Racial implications in some episodes. (Example: implying that Monica was racist just because she had never been in black human form)
What an Idiot: You DID have to feel bad for the victim (as well as his parents) in the episode "The Peacemaker", but at the same time, you realize he was also this in the end. A teenage boy with a troubled past involving drug abuse is graduating from high school and is also dealing with his parents' failing marriage. So, the kid one day is in a bank when it is robbed at gunpoint. One of the robbers tells him to give him the money (which even Andrew urges the boy to do so that he would not be needed), but he refuses, saying that he needs it for an important reason. He is shot because of this and dies. So while the parents are blaming each other and themselves for his death and fearful he needed the money to buy drugs, Andrew and an independent filmmaker come to them one night and gives them what he needed the money for; to pay him off for a tape made for them to remind them of him as he's away at college and fonder memories of them in an attempt to stay together. It worked. However, you have to wonder why he gave up his life just to keep his folks together when he could have gotten the money some other way (maybe through the Angels' help, perhaps?), gave them the tape and live.