Most horrible instance per expansion. (MMO Copycat)

[pengupuff]

Vanilla: Blackrock Depths. God damn, this shit is a twisted labyrinth of misery that I can't navigate to this day.
Burning Crusade: Mana-tombs. Boring. Generic.
WotLK: The Occulus. The concept was cool, but it got annoying after a while.
Cataclysm: All of them...? Lol. I guess I hate ZG/ZA the most.

[Kayb]

Vanilla: all the Maraudon, Dire Maul and Blackrock dungeons. bah they just all sucked.
BC: has to be all the Auchindoun ones
Wrath: Halls of Stone and Lightning. The universe hates me, because 98% of the time these are the only two the dungeon finder would ever bring up.
Cata: Can't say I particularly like any of them to be honest. And again, 99.99% of the time, Lost City of the Tolvir would come up in the finder. Ugh.

[Curzon]

Classic: Mauradon...even just getting to the instance was confusing...and still is.
BC: Aucheneai Crypts - Shirrak...just, no
Wrath: Can't say I ever hated any
Cata: Stonecore...Ozruk...just /fetal position

[Fworbin]

Vanilla: Gonna have to go with anything Blackrock. Usually not even worth trying to Pug it.

BC: Mm..Blood Furnace. Particularly with people who were a bit low to get in. The mines..Oh god, the mines.. Nowadays, anything early on, because of the Dk tanks who can't be bothered to understand this strange new 'threat' thing, or that the pointy end of the sword goes in the red orcs, as opposed to, say, my kidneys.. (No offense to those who do know the difference, of course.)

Wrath: None that I can think of..Then again, I'm quite fond of Wrath, possibly because I stopped being awful at the game during it. =p

Cata: Heroic. Stonecore. So. Much. Hate.

[Zuilu]

Vanilla: Gnomer. Oh my god Gnomer. I hated Gnomer SO MUCH. BRD was a close second though, because as others have said, it'd take half a day. e.e
Burning Crusade: Hellfire Ramparts. I just didnt get this place. It was boring, it was bland, it wasn't a good way to get fresh-outland players into the new zone.
Wrath of the Lich King: Halls of Lightning/Halls of Stone. I fucking hate these two. Never again.
Cataclysm: Close tie with Grim Batol and Stonecore.

[Aeliel]

Vanilla: tie between Gnomeregan, Wailing Caverns, Maraudon and the old version of Sunken Temple (not the neutered version they put in with Cataclysm, that one is nice and quick). I keep getting lost in BRD, too, but I can't help it - I love that one.

BC: Old Hillsbrad. Lovely from a lore perspective, but good heavens, HURRY THE HELL UP, THRALL. There's tons of runner ups here, especially if we count the heroic versions that people were epic fail at (H-Mana Tombs, H-Arcatraz, H-Shadow Labyrinth, H-Shattered Halls, hell even H-Mechanaar, what with the second boss).

WotLK: Halls of Stone. No contest. The Brann event can go die in a fire. Also Culling of Stratholme with Arthas the slowpoke. Halls of Reflection also made me want to punch kittens more often than not when people just wouldn't understand how it worked.

Cataclysm: can't think of one I really hate. Possibly Zul'Aman, because half the time I zone into it on my tank main I get scrubs in half blue, half green gear who used PVP BoEs to cheat the ilvl checker and proceed to demand a bear run. >< Stonecore makes me cringe when I'm not on a tank character, because Ozruk is so very unforgiving if the tank has no clue.

[Monica Gems]

Classic; Blackrock. While the LFD has shortened it, it's still way too freakin' long.

BC; SLab. Murmur still gives me nightmares sometimes. Steamvault is a catastrophically close 2nd.

Wrath; HoR. Everyone wanted to cram into that tiny corner because no one wanted to CC. Trap/Shackle/Pally the hunter. Silence the mage to bring her to the tank. This was what my guild figured out to do our very first time in there - not rocket surgery. And that was the first sign that everything we learned in BC and Classic about CC had ben forgotten. Not a fan of Nexus or VH, but they definitely weren't "worst".

Cata; Tie between Deadmines and Grim Batol. I always get in a group where no one can use the reaper (I DC when I use it, not every vehicle, just the vehicles in there, including the cannons). In GB, I always get a group that A] Can't move out of the giant bright dragon breath, or can't (or won't) dps adds on last boss. Blackrock is a close second because watching Corla's debuff beams is hard, apparently. (Also I hate kiting the adds, but that's never a close fight, just boring.) Fortunately 2 of the boss encounters I listed are skippable.

[Aeliel]

Trap/Shackle/Pally the hunter. Silence the mage to bring her to the tank. This was what my guild figured out to do our very first time in there - not rocket surgery.

Yeah, that works for a guild group, but when you have a random PuG where people can't be bothered CCing and can't be bothered interrupting - never mind that you wouldn't necessarily get a group composition with any interrupters or with any CC that worked on undead - LoSing them in the corner becomes your only option.

[Monica Gems]

Trap/Shackle/Pally the hunter. Silence the mage to bring her to the tank. This was what my guild figured out to do our very first time in there - not rocket surgery.

Yeah, that works for a guild group, but when you have a random PuG where people can't be bothered CCing and can't be bothered interrupting - never mind that you wouldn't necessarily get a group composition with any interrupters or with any CC that worked on undead - LoSing them in the corner becomes your only option.

We were pugging 2 ppl, wiped once, then decided to CC; war tank, druid heals, hunter dps. "Hey guys, we're having hunter trap square and the warrior will grab the mage with heroic throw."

But your post is exactly my point; we're forced to LoS (and improperly because the DPS and healer will cram in there, unable to see, while the tank stands in the opening going "hurr durr dey r jus shottin y dey no com 2 me??" hey pal, you have to LoS too!), and everyone takes a bunch of damage from the close quarters. When I got thrown in there, I always made the tank try it in the open, just once, before we huddled like scared cats in a closet. Most of them walked away saying they liked it much better; easier to see, easier to move, etc. LoSing was just as messy, if not messier, than doing it in the open.

The odds of a group having no CC whatsoever is pretty slim; rogue has kick, hunter had at least trap, pally undead stun, priest shackle, mage counterspell, DK had 2 silences and death grip, warriors have a silence/spell lock if I recall, shammy has wind shear.. and I'm not versed enough about 'locks and druids to remember what they could do back at 80. Everyone could do something, but you'd have to actually remind them the spell exists.

For example, if you had a priest and a dk...
/zone in. look at group comp.
PL: priest shackle hunter, dk silence mage. r?

That's why it gets my vote; common sense was flung out the window.

[Aeliel]

Oh, I agree that doing it out in the open is better - if the people in the group have a clue. That's my point. Most HoR PuGs I got thrown into were all "hurr durr wuts cc?" or "herp derp wuts interupt?" - even if I told them exactly what spell to use and on which target, the vast majority wouldn't. They were far too concerned with tunnel vision style DPS to bother.

[Pokerfase]

Vanilla: I didn't do much in the way of instances in Vanilla.
Burning Crusade: Same with BC. I didn't run stuff enough to develop a hatred for any instance.
WotLK: Halls of Reflection. It's amazing with a competent PuG... good luck getting one. If your PuG doesn't do jack, then the instance will make you want to pull your hair out.
Cataclysm: Tie between Stonecore and Blackrock Caverns on Heroic. Ozruk's a bitch for most PuGs, and Blackrock Caverns has two group-breaking bosses: Corla and Beauty.

I don't really have a problem with Grim Batol, unlike many other posters. ZG's not up there (despite Jin'do the Groupbreaker) because it has some pretty interesting gimmicks.

[Davarra]

They were far too concerned with tunnel vision style DPS to bother.

Way too many groups boot you if you don't. All they care about is numbers, and it doesn't matter if you saved their behinds 20 times, if your dps isn't up to their arbitrary standards you get abused or punted.

Vanilla: Gotta go with Gnomer.
Burning Crusade: Much as I LIKE the instance itself, Auchenai Crypts. Too many healers drop the ball on cleanup healing after the floating eyeball boss.
WotLK: HoR. What more needs to be said?
Cataclysm: HDM tends to be truly nightmarish still, entirely too often. Grim Batol also.

[Sarantha]

Vanilla: Stratholme, only because I ran it over and over with guildies in an attempt to get Baron's horse.
BC: Crypts. Oh, Loki, Auchenai Crypts. I HATE IT SO MUCH!!!!!!! I did it on each toon only to get the Thrall's Granny quest done, but never set foot in there again.
WOTLK: Come on, really? Do you have to ask? Oculus. Even after nerfs...I HATED RIDING THOSE DAMN DRAGONS! HoR comes in a close second, because I hate running from Arthas while Sylvanas shoots puny arrows at ice walls when I could be fireballing that shit instead and she could use her epic leetness to help kill the mobs.
Cata: Every dungeon, because they just suck. Honestly. I hate Cata. I want to go back to BC. Crypts was the only bad part of BC. That instance with all the Egyptian Gods as bosses really sucks though, if I have to pick. Halls of something, I'm sure. If it has Halls in its name, its bound to suck.

[Varethyn]

It's been some time but I think it'd be something like this:

Classic: BRD. Always got lost, even while soloing. Gnomer and BRS come close behind for the same reason.
TBC: Can't really say I hated any of them. Guess I'll say Sethekk Halls just because it took me two years to get my Raven Lord ._.
WotLK: Any of the Frozen Halls 5-mans. I like the instances themselves but such bad experiences with PuGs...
Cata: Running through them, I actually like all of the Cata dungeons, but SFK is just so... boring now. Apart from the skippable Baron Silverlane ALL the bosses LOOK THE SAME. Okay the original had three worgen bosses but at least they looked different. I much preferred the original. I miss the giant Fenrus the Devourer, and Arugal and his mind-control that turned you into a worgen.

[Schwert]

Oh boy. My seething rage comes worth from the inner depths of the black soul these dungeons formed for me.

Vanilla:
Blackrock Depths. I despise it with every fibre of my being. Every. Single. One. I intentionally quest to avoid getting it in LFD on any alts I level because I hate it so much. Not to mention people don't know where they're going and it usually never gets finished.

Burning Crusade:
Hellfire Ramparts. You can only run something so many times with so many Death Knights before you never want to see it again.

WotLK:
Occulus. I dreaded trying to PuG this place trying to get my Red Protodrake because I was demanded to do exactly the opposite of what I made the group for. ((No, I am NOT riding the Green Drake. I said so when I invited you.))

Cataclysm:
Lost City of Tol'vir. I generally don't like the desert in the first place and I just constantly kept getting the place non-stop for a couple of months. No more. No...more...

[Royi]

I'm suprised at the amount of Gnomer and BRD ones. I guess its because if you don't know where to go in those instances or know the ins and outs, they can be very annoying. BRD as a whole has so many bosses, and running through the entire place after doing a Jailbreak was quite fun.

Gnomer I loved since I knew the routes to take and those triprunner dungerees were too good to beat for quite a few levels.

I disliked running Scholomance, because well that instance could take 2 hours, I think I was in there 4 once. All for a 1/8 chance at the time for my Rogue helm to drop (it never did).

~~~~~~~~~~~~~

I really wish they would allow you to queue for ALL heroics now though (including ZA / ZG) and get the same Valor point rewards. Heck I haven't done half the regular heorics on my hunter because I fast tracked into ZA/ZG.

[Kalliope]

I'm suprised at the amount of Gnomer and BRD ones. I guess its because if you don't know where to go in those instances or know the ins and outs, they can be very annoying. BRD as a whole has so many bosses, and running through the entire place after doing a Jailbreak was quite fun.

In many of these cases, it's more the groups making the instances bad rather than the instances themselves. All of them are easy, regardless of length, if your group knows what it's doing and those members who don't know follow those who do.

[Schwert]

I'm suprised at the amount of Gnomer and BRD ones. I guess its because if you don't know where to go in those instances or know the ins and outs, they can be very annoying. BRD as a whole has so many bosses, and running through the entire place after doing a Jailbreak was quite fun.

In many of these cases, it's more the groups making the instances bad rather than the instances themselves. All of them are easy, regardless of length, if your group knows what it's doing and those members who don't know follow those who do.

This. I've done ZG's that have only lasted a half hour and they really made me /enjoy/ the instance because I'm not sitting there wasting my gold because the hunter can't kite or the priest doesn't know how to bubble.

Also; I'm tempted to rally a naked BRD LFD group sometime. ONWARDS TO NEFARIAN. REMOVE THY CLOTHING. THY BORING SHALL BE GONE.

[Sarantha]

To clarify my hatred of Stratholme, this is when it took 2 hours to complete and we ran it over and over for Baron's mount and it never dropped. The instance itself is still very well done and I would like a heroic version, tbh, because it truly is epic. Stratholme should not be forgotten, just...redone a little. And the drop rate on Baron's mount upped.

As for least-well done instance in vanilla, Wailing Caverns. WTF? A maze? I'm playing WoW, not friggin nintendo games. You would not believe how many groups get lost in there, no matter how many times I tell them to LOOK AT THE MAP! Or, if they can't figure that out, LISTEN TO ME! /facepalm at Wailing Caverns. WTF was Blizz smoking the day they made that instance?

[Morven]

Worse, WC is a 3-D maze, so even more confusing for your random PuG.

I'm still kind of upset they ruined Sunken Temple, too. I don't see what the problem was with the previous; it wasn't all that hard.