QuickTime Events. Ban them. In outer space. In the hottest hell. In the deepest dungeon. These things are evil I tell you.

Tutorial hint boxes that constantly pop up, pause the gameplay, or take control away from the player. They are annoying, and a cheap way to teach the player how to play your game. Don't do this. Teach the player about your game through the gameplay. Give the player a hint and let them figure things out themselves.

Cutscenes you can't skip, which can be especially annoying when a game doesn't have good checkpoint placement. It gets very annoying very fast.

Quicktime events. They're lazy as hell.

Unbalanced difficulty levels or lazy difficulty balancing. I'll use FEAR 2 as an example here. Easy is laughable, but normal is also way too easy. Goons drop quickly and I almost never get a scratch on me. So, after beating it on Normal I went ahead and beat it on Hard, only to be greeted with getting killed in one to two hits constantly. The difficulty spike between normal and hard is so out of whack it's frustrating. Compare that with FEAR's extreme difficulty, which I completed and had a very great time with. Everything in the first game feels better balanced overall.

Lots of FPS are guilty of lazy difficulty balancing where they just make the enemies hit sponges on the harder difficulties and call it a day. Some games are also just unbalanced messes overall. I hurt a lot of people's feelings when I bring up that the original Shadow Warrior is a laughable mess. Hitscan enemies with no delay before they start firing at you, that drain your health extremely quickly, and have no fire frames for when they shoot a missile or grenade at you making it impossible to read their attacks as it just shoots out of their chest? Rise of the Triad pulled that same shit.

Yet, every other enemy type is a giant pushover, your weapons are OP, especially the grenade launcher, your items are near useless save for the invincibility and medkit, and the bosses are complete pushovers and in true Build engine fashion extremely exploitable. I didn't fire a single bullet at the final boss and I took him down in less then 5 minutes. When the game's most deadly enemy is the lowly goon that's garbage.

On the other side of the spectrum you have a game like Quake 2 which is laughably easy (and dull). All the enemies have your typical pain chance frames where their attack or walk gets cancelled and they flinch, but they also have frames of them falling on their ass if you hurt them enough... I went through that whole game on Hard, not falling below 50 health due to the OP power shield that always works as long as you have Cell ammo, and just running into their faces with the SSG. The first shot knocks them on their ass, the next gibs them. They can't even attack me. Similarly in DOOM 3 the spawns are so predictable and the enemies walk so slowly that all you have to do is run up to any imp and shoot it in the face with your shotgun. It's too busy roaring at you to attack and one shot puts it down.

That's probably my #1 complaint, and that's usually just down to not planning things out well or including things to the sake of inclusion.

Stupid control scheme

Anyone remember double dragon for nes?
Facing right, a for punch, b for kick and reversed when facing left.

Bottomless insta-death pit with flying annoying enemies (looking at you Medusa head from old castlevania)

Universal ammo from deus ex invisible war. Handgun and rocket launcher share the same ammo pool? Whose idea is that?

I still don't quite understand. I, and I think the others who asked, are thinking of narrative experiences when we imagine "bad endings". You are speaking of the game not providing what it promised.

For example, Red Dead Redemption in terms of gameplay, is about being a cowboy in the wild west and doing most things we associate we that, and it definitely delivers. In narrative terms, it's about a man forced to hunt down his former brothers-in-arms in order to ensure the safety of his family. He succeeds, and his family is safe. Yet those who've played it know the ending is still quite sad. Was RDR a scam? Or do you divorce gameplay expectations from narrative ones?

People have mentioned unskippable cutscenes, but there's something even worse: an unskippable cutscene followed by a three phase boss fight (with no save or checkpoint in between), with the third phase having an attack that will very likely cause a game over on a player's first attempt.

Final Fantasy X did what I describe: a 5 minute cutscene, followed by a 3 phase battle, with the third phase starting with the boss using an attack that instantly kills anyone who isn't under zombie status (and a typical player, not expecting this attack, is likely to be curing zombie when it's inflected early in the battle).

Another cardinal sin is punishing the player for progressing through the game. In Final Fantasy 7, there is one particular character whose limit breaks, unlike those of other characters, are healing rather than offensive. Unfortunately, once you reach a certain point in the game, the game takes away that character, and never gives you the character back, taking away an interesting strategic option. Other similar issues come when the game doesn't let you return to earlier areas past a certain point, and when games have permanent missables. (Permanent missables have always felt like sloppy game design to me.)

Don't look directly at it. You'll turn into a pillar of salt.

Being the one to save the world.

Oh come on, her limit break is too overpower. She casting "planet protector" will make every battle a walk in the park, including last boss. From storyline point of view her death is important and from gameplay pof if she lives through the end they would need to nerf down her ability massively.

Still, her death sucks a lot
Can't agree more :)

^This

And the inability to save freely. Checkpoints are nice and dandy to have ... but to remove the ability to save wherever you want is just an annoying artificial way to increase the difficulty and is a very bad inheritance from when console games couldn't save. On the PC this has always been a cardinal sin. On modern consoles it's unnecessary too. Whoever decides to publish a game without save function should be forbidden to publish anything and be sent back to game design school.

Yes, it is possible to write a gripping 'bad' ending that feels deserved or at least logical or tragic. But there are also bad endings which come out of nowhere and just feel forced and like screwing with player. Especially Divinity 2 - Ego Draconis felt like it's developers wanted to punish all their players for playing their game. Lots of railroading, glaringly stupid decisions that your character took without the possibility to influence them culminating in a final 'screw you for playing!'.
I know they amended that ending in the Dragon Knight Saga, following massive fan protests. But by that time I had already decided not to throw more money at Larian and the original game should still be studied by all developers as a warning example of how not to do things.

Unskippable cutscenes.

Throwing a dozen identical easy combats against you just to whittle down your resources, instead of one big difficult battle.

Not being allowed to remap keyboard.

Forced 3rd person view instead of being able to switch between 1st and 3rd.

Too many strategy games are ruined by poor AI.

Especially forced 3rd person view that obscures half the screen. (Dead Space)

What an annoying page. I thought it was a troll attempt making you waste your life so I scrolled down immediately only to figure out what it was. Apparently I'm self-centered and commitment-phobic the way I handled that although if I had I known it wasn't a troll attempt I would probably have read at least a third, perhaps more. Why do you consider it a scam?

I used to abhor cliffhangers, now I adore them, they are so annoying but in a good way. Predictable and generic is probably the worst regardless of it's a typical happy, sad, bittersweat or something more open with a little bit of all. I want a unique and surprising ending given the amount of games, books and TV I've enjoyed.

More generally, a 3 phase bossfight with no way to retry (temporary save, retry option...) just the phase you got killed in. Because I just LOVE to play AGAIN the phases 1 and 2 just to get one shotted once more by the boss' "ultimate form"

Sure, it adds tension ("please don't screw up and make me play again that 20 minutes bossfight, please don't..."), but the 3rd or 4th time? I'll just drop the game and play another one.

Also : Featuring Lagaf'.

Seriously guys. Seriously. What next, a game featuring the singer Carlos ?

Oh.