Oh gosh. I'll likely do multiple small posts spaced out so that I don't clog the thread, but here goes -
1. Creative talents injecting personal social commentary:
I think we've all seen this before, at least to some extent. The writer has made the decision that they're going to turn their work into an "author tract", and as such they're going to vent their personal feelings about a topic, no matter how appropriate the situation is or how little research the writer has done on the issue. The heroes all regurgitate whatever the author's social and political beliefs are, and the villains are everyone who say anything but. Nobody can simply disagree on an issue; the opposing party has to be shown in the worst light possible.
If a character is in favor of gun control, they can't be a mother who lost her child to a gang brawl; they have to be a fascist whose ultimate goal is complete disarmament of the populace so that the government can take over. If a character opposes gun control, they can't be a humble rancher who needs to drop the occasional bear or wolf that's going after his cattle; they have to be a right-wing militia member who expects the government to go Waco on him at any given moment. Et cetra.
2. "Greatest Hits" soundtracks:
Something I see far too often in "period" pieces is the soundtrack consisting of only those songs that are still remembered at the time the film is made, regardless of how popular the song was back in the day or whether the characters would actually listen to that kind of music.
For example, imagine a hypothetical film about a group of heavy metal fans in the 1980s. 9 for 10, the soundtrack's going to include acts like Quiet Riot, Def Leppard, Bon Jovi, and perhaps Twisted Sister... specifically, the two or three songs the general public knows from each band. KISS? Judas Priest? Accept? Loudness? Alice Cooper? Less well known songs from the more mainstream metal bands? No dice.
3. Mandatory "Girl Power" episodes:
I understand that writers want to show off the fact that the female cast members are competent in their own right, especially in their areas of expertise. Problem is, I've seen far too many situations past and present where the writers decided that the best way to do so was to hand the male characters the "idiot ball" or otherwise go to some absurd lengths to remove any competence or relevance they have. The end result is that instead of depicting the female characters as competent, it depicts the male characters as maroons.
For example, the classic G. I. Joe episode "Cobra's Candidate" sees the male members of a Joe task force captured by Cobra, leaving the two female members to complete the mission. How are they captured? The Dreadnoks somehow succeeded in getting ATVs up to the roof of an apartment building in the middle of a major city, then jumped those ATVs from rooftop to rooftop until they were able to get to the building the guys were climbing up... in the process landing their ATVs so that the back tires were spinning out on the fire escape ladder the Joes were trying to climb, ultimately causing the ladder to tear free and fall down on them. There aren't enough facepalms to cover how much the writers had to stretch reality to make this happen. Rosie O'Donnell has a better chance of winning the next Miss America competition than these events have of happening in real life.
4. Gore Horror:
Perhaps the biggest thing burning me out on horror films is the fact that entirely too many mainstream jobs feel the need to make the content as graphic and bloody as possible. It's almost like it's not a horror film unless someone's getting disemboweled right in front of the camera. Not only do people get desensitized to this kind of nonsense after a while, it can even create a backlash among people who know what that kind of stuff looks like and also trigger people who have legitimate anxiety or PTSD issues.
I'd love to see some old-school Hitchcock psychological horror come back around, one where they don't telegraph anything but where all of the pieces and clues are still there regardless.