I have recently been working on dungeons in my Athlis mod, one of the very last steps to completion. I've already completed a few, but before I go off on an epic modding-spree of dungeonness I want to know what YOU THE PLAYER like most about dungeons. This way I can continue to build with what appeals to you most.

Personaly I prefer all of the above, however the lengthiness of a dungeon can sometimes put a damper on the amount of detail crammed in - for as much as I'd like to I don't want to spend weeks at a time on only one dungeon. Another thing is that in Morrowind I felt that most caves and dungeons served little to no purpose. Sure it was fun raiding them - but in the end you are just a few potions poorer and there was nothing special obtained.

So let me hear what you think!

The atmosphere is important for dungeons. I use the haunted tombs mod to help with my game. Secrets are important too. They give you reasons to look around.

The parameters I'd advise, if anything, are:

+ Small size.

+ Unique design. (Something that stands out against the vanilla dungeons.)

+ Few but fearsome enemies.

+ Creepy, low volume noises.

+ Dim, flickering lights. (That have real reason to be wherever they are.)

+ Hidden compartments. (The kind that are revealed by pressing on rocks and such. Real Indiana Jones-style. )

+ Traps. (Not too elaborate, stuff like spikes suddenly shooting up out of the floor.)

Damnit, now I feel like building a cave full of monsters. Like I don't have enough to do.

Here my few Cents:

From my old D&D mates, a DM, used a very sound design philosophy when it came to dungeons:

'The suffering the Players and their Characters go tru ( Fights, traps, nerves and so on) must pay off at the end. '
Meaning loot and rewards that compensate.

-Keep it exciting.
-Don't bee afraid to make the player work.
( if he has to traverse A to B and back again, so be it)
-Less is more
-Use your own phobias against the players.
( small spaces; lots of spiders; creepy music, silent hill atmosphere ( fog and sound ), Water (lots of underwater passages.
-Loot that pays off, but not in a too big way.
-Dead adventurers.
( one of my faves. Nothing says better 'your the next', like a fresh corpse leaning on the wall - if possible with some diary or random scribbles on it)

Atmosphere first.
Secrets and hidden fun, come in second.

Size, big treasure, bosses... not important if you make the dungeon memorable.

Think of it this way.... Years after playing a mod, what do you remember about? How big the dungeon was or the uber treasure?
Not likely.
More than often you'll remember the unique style and "feeling" you got from the mod... not each battle or chest.

Also, scripted events go a long way to make a mod memorable. I recommend them

GREAT feedback!! Keep it coming!!

Haha, the last option is the best. Get on it man!!

As everyone else for me, it's the atmosphere, killing the same uglies in an repetitive environment lead to boredom.

For a good dungeon :

Forget the size, it's the layout who is important, I don't want making 20 miles underground, I want searching and battling my way through a disorienting maze.

Details : whatever is the environment of the dungeon ( velothi, telvanni, loony,..) there is no difference if I have my bottom kicked by cake monsters in Sheogorath's bakery or in a smuggler cave where you can spot a small altar built by the local cleric between two rubble and read a few personal diaries.

Challenge isn't only made by battling a daedric prince with a teaspoon, try to create some enemies while no overly powerful who need a more subtle strategy to be defeated than "hack or spell the s**t outta them"
( few hp but numerous immunity and a not so glaring but very effective weak spot, creature summoning others, sneaking past them,etc...).

Secrets : while not mandatory, either as secrets stashes or unlocking news surprises with scripted conditions they improve a lot the (re)playability of a plug-in.

Bossfights : as one who was put to sleep with "lullaby" such as Unreal, Half Life, and others Baldur's Gate, they are for me a must have.
However such a pinnacle of adventuring is never done by simply putting the player aginst an uber monster, this is a recipe for disaster.
The first thing to offer in a boos fight must surprise the player, it's even mandatory to make it a fight to death, but a boss sequence must offer a different challenge from the rest of the module, something where everything the player had done and more over will test the player.
A good way to introduce a boss fight is presented http://www.unrealsp.org/community/leveldesign/tutorials/bossfights.html. It's for Unreal 1 but the spirit is the same for every game, a boss fight must be the crowing jewel of a mod, his apex, otherwise forget about it.

Lights : often overlooked, playing with the light is the quickest and more efficient way to create or reinforce a mood or the feeling of a mod. So use and abuse of them.

For a good sample of classics but detailled dungeons filled with a few secrets look for http://planetelderscrolls.gamespy.com/View.php?view=User.EntriesListing&id=6853.

For the badasses of Dungeon crawling ( ambiance, atmosphere, detail, Bosses, traps and bosses) here is the top three : the founding father http://planetelderscrolls.gamespy.com/View.php?view=Mods.Detail&id=9230, the eternal number one http://planetelderscrolls.gamespy.com/View.php?view=Mods.Detail&id=6068, different but awesome http://planetelderscrolls.gamespy.com/View.php?view=Mods.Detail&id=6270.

Two of my favorites : http://planetelderscrolls.gamespy.com/View.php?view=Mods.Detail&id=4745 and http://planetelderscrolls.gamespy.com/View.php?view=Mods.Detail&id=7447.