Zelda - The Wind Waker on Nintendo DS (at least I *think* it was the wind waker), for having to do the same temple over and over again. I know there's supposed to be a point were you can skip part of the temple, but that mechanic completely ruiend it for me.

Enslaved - Odyssey to the west, for having a protagonist that first enslaves another character and then says sorry. The general behaviour of that character enraged me to such an extent that I immediately quit playing. Luckily it was only the demo on PS3 and not a game I bought.

Thief 1, the supernatural angle. I don't want to rob crypts or whatever trying to avoid skeletons, zombies and demons. I want to be a thief robbing banks, mansions, police stations etc. That's why I prefer the 2nd entry in the series over the first.

Gothic 3 was a mess when it came out in 2006, the most bug-ridden game I've ever played.
I actually had to stop after about ten hours, because I couldn't take it anymore. The game is very different from the two first games of the series anyway, the second one being my favorite game of all time, so it had a though start with me on that alone, but the technical problems ruined it for me at the time.
Years later, with the Community Patch fixing everything, I enjoyed it greatly. The music is without a doubt the outstanding feature.

What, no one has mentioned Ultima I's interlude in space? I've never liked shooters; don't force me to play a minigame just to reach the ending.

Yeah I'm not much fond of it either. I seem to recall that a similar system of just whisking the player away to some other place was used in FarCry 3, and was the reason I stopped playing that game.

You have played something as batshit insane as VANGERS long enough to be annoyed by the grinding? Color me impressed.

Not to mention that some of us have limited time,and can't devote hours at a sitting to a diffiuclt part of a game.

Mario Party 1's "rotate the controller" mechanic basically killed the game forever, even in redistribution. Nintendo won't even re-release the seminal game, because it has done too much real harm to controllers and hands alike. Purgatory! Purgatory!

Hate to say it, but you had better not plan on playing many major games if you can't put up with DRM.I don't like it either, but you have to be realistic.

Serious Sam. A lot of fun unitl the final level. I am still puzzled how you can win without cheating. Incredibly difficult.

Oh god I remember that. I think I wrecked the analog sticks on both of my N64 controllers with that, and frequently ripped the skin off the palm of my hand (anything for victory!). I believe that's why analog sticks are rubbery now... though you don't see the rapidly rotate the analog stick mini games any more I don't think (it's been years since I bought a Mario Party game or something similar)

I'm not sure I've played any games that I would say were ruined by a single aspect. I don't get put off games all that readily.

For me they have another game breaking aspect: Windows only (with DirectX10-12, everything below usually works great via WINE).
I'm a happy Linux gamer with way more interest in indies and classics anyway. ;)

No One Lives Forever 2

Respawning enemies. Not totally ruined but inferior to the first one, like doing your best super spy to clear an area and more guys show up is not cool.

Serious Sam: The First Encounter? By final level, do you mean the one inside the pyramid? Apparently it can be done as I have finished it at least a couple of times, playing on the second hardest difficulty level (I didn't want to play in the very hardest difficulty as that makes enemies partially invisible, which to me just felt like a dumb way to make the game harder).

I recall the last fight inside the pyramid was quite tricky in some way (I can't recall in what way), but yeah it can be done.

I will personally rate e.g. the Far Cry final boss fight as much more frustrating.

That has ruined a lot of games.