(Yes, this is a response to the other topic.)

For me, I would say a stealth sequence in a non-stealth game. That actually ruined Zelda: Ocarina of Time for me.

Off-disk copy protection checks where they give you a book/page/picture/wheel to reference and you have to answer questions.

Important notes/lore is located outside of the game installation itself (SSI's D&D games come to mind)

Bad UI

Bad controls

Really crappy bland voice acting

Adding on to the whole stealth thing, stealth sequences where simply being seen gets you thrown out. Stealth isn't so bad if being seen isn't essentially instant death. (Metroid: Zero Mission, for example, was a bit better about this.)

Another thing: In games where you get more powerful as you progress, parts of the game where you are unable to use that power because the game changes genre. In an RPG, I would rather have a fight (in which stats matter) than a mini-game (in which stats don't).

Similar and repetitive quests/missions. They are not annoying in short games, but in long RPGs (or other games), they're boring and frustrating.

Game developers thinking their games have got infinite replay value just because the level layout is randomly/procedurally generated each time you start a new game, with no other changes to the gameplay.

ROMANCING in my RPGs - http://forums.obsidian.net/topic/44687-romances-in-nwn-2-and-rpgs-in-general/page-7?p=725311#entry725311

ELVES in RPG-s.

The not so little things:

Crappy DRM. Nope, no sale for you derplings.

Censorship: Whether it's state or public pressure, it's something I really hate, there is no fucking need for it when there's an 18+ rating in place (and adults hardly should be affected by sex or violece in videogames, don't like it, don't buy it).

Bad Ports: yes, we know already it was designed for console first, still not an excuse.

Being a buggy piece of shit: Yes, most games have bugs on release, but being an unplayble mess, and then expecting customers to wait for month for bugfiex that may never come... that definitively shouldn't be a tolerated business model.

The little things

Unrebindable controls: Some people don't like your standard keybindings, and on PC, there is frankly no reason to not have such an option, especially in more complex games. I'd say QTEs in general, they just seem more of a pain in the ass than anything else now (with the novelty of the past long gone by).

Edit: spelling + somewhat misread the title

Skyrim and those "Radiant Quests" comes to mind instantly, although Skyrim doesn't take a lot of time to finish 100%, except those same pesky radiant pieces of S***

The ones in Fallout 4 are even worse. You don't even notice they're radiant until you've done some of them as they feel as a regular part of the faction questline.

Timed dialogue responses, especially in what is supposed to be an adventure game Telltale.
Bland and uninteresting worlds, I'm looking at you Shadow of Mordor and W3.

*DRM. A simple offline CD-check is no problem, but anything beyond is unacceptable... tried it once on the behalf of millions of blind people, got burned in the end.
*DRM. No, I'm not making an account and get an internet connection just so I can play the game I paid for, you corporate fools.
*DRM. No, Steam is not the least of evils or Uplay the worst of evils. 'The least of evils' is still evil.

Okay, enough already!

*Lack of updates on a certain store - Developer X saying that they will not update Game Y on Store Z because Store Z is inferior to Store A is inexcusable, especially if you already released Game Y on Store Z.
*Sudden spikes in difficulty - Freedom Planet... Freedom Planet... Freedom Planet... I love you, but please, don't put a nigh-difficult level almost right after an easy level and then put an easy level after a nigh-difficult level.
*Crashes like no tomorrow - Hotline Miami... please don't crash regularly.

Bad AI, though silly AI can sometimes offer entertainment in its own weird way. Nothing more fun that shooting at an enemy, only to watch as he spazzes out and crashes his head into the wall, getting stuck in the process and flopping around in a texture blob of madness.

Unskippable cut scenes in games. Is unskippable a word? Well, it is now.

Poor UI formats. Nothing like having to learn coding, geometry and algebra all over again just because some dev couldn't figure out an easy way to show me where my goddamn health potions are.

Characters that are inserted into games that are clearly there just for showcasing a piece of merchandise, a future DLC, or worse... the political beliefs of some dev that just to make some goddamn point by making the dude who fixes my car in the game as a reformed sex offender who just got a bad wrap because... blah blah blah. I don't care, don't make superfluous, bland characters and then tell me that Ronnie the gay schizophrenic gun merchant is there to help me upgrade my grenade launcher. Fuck Ronnie and show me what's for sell at the Ammo-mart. I got things to see and alien invaders to kill. Don't waste my time by putting in talking sea creatures in my FPS because you're fighting the good fight trying to get lobsters the right to vote. I don't care. Fuck you, fuck the lobsters, now give me what you got and piss off.

DLC. Just lotsa no all around there.

On that note, Telltale's inventory system is one of the worst I've encountered in any adventure game. I don't know if they've changed it by now, since I haven't played any of their recent games, but in the Tales of Monkey Island games at least, in order to combine two inventory items, you have to first place one in a slot designated for the purpose, then place the other in another designated slot, then press a button between the two slots. In a game where puzzle solutions often require the combination of two unlikely objects, and where you are often carrying more than twenty objects at a time, that approach gets really old really quickly.

Heterosexual romances. They are way to common, and I prefer my games to be without them. It seems that every time there is a male character and a female character in a game, there has to be some romances. (For whatever reason, I don't have this issue with lesbian romance. Perhaps it's at least partly because they're less common?)

When the game mechanics favor male characters (SSI gold box games) or male characters get superior equipment options than female characters (Elminage Gothic, but fortunately that shouldn't be too hard to mod out).

Of note, I will refuse to play any tabletop AD&D 1st edition game that enforces the limit on female strength. If asked to DM such a game, I will explicitly house rule those limits away.