I think it would be really cool to have a quest mod where you don't get quest updates every itty bitty step of the way. Most quests allow you to keep and read the notes, diaries, etc. written by the NPCs, but you never have to, because the journal updates basically just spoon feed everything to you.

Like, here's a rundown of how the quest might work (of course, it doesn't have to be this plot; it can be next to anything, so long as you don't get actual journal updates).

You find a corpse near a place that you probably frequent... like the Imperial City Market District. On this corpse's body, you find a note. The note tells you of the existence of a "Great Treasure," but doesn't tell you its exact whereabouts, only a vague clue. You get no journal update, and there is no quest, not even in the Construction Set. You have to actually read the note to be any the wiser of anything.

So, you go to this genera area that the note speaks of, and you see some kind of cryptic message carved into the wall, written in a real, but rare and obscure language, such as... say... Tagalog (and yes, that's an actual, real language that people actually speak in obscure parts of the world).

The message is carved into the wall, but your character cannot interact with it, you get no journal updates, and, in fact, the game's engine will soon forget that you were ever there. You just have to read it, and jot it down, yourself, on a real sheet of paper.

So, you have to use a computer to translate the message (of course, there would be some kind of clue to tell you that it's a real language that you need to actually translate). They tell you of six special containers throughout Cyrodiil. Place certain items into each container, and come back in 24 hours to each container, and a note will have magically appeared in the containers. You get no hint that anything happened after 24 hours.

Read these notes and you'll get a clue as to a password. Again, as you may have guessed, no journal updates. You just have to actually read them.

Four clues help you decypher what the password is, and two clues tell you where you're supposed to go to enter the clues.

Go to the specified location, activate the door, and it will ask for the password. Enter the password, and you'll be taken to an alternate dimension (with a portal back to Cyrodiil, of course) where you can fight a boss, and loot the Great Treasure off his body after you've beaten him.

Of course, it doesn't have to be anything like that. The main idea is that you have to actually be observant of the world around you, because the journal log will give you no hints... you have to figure everything out yourself. The example I just gave is merely to explain what I'm talking about.

I think that would be awesome!

Blade of the Haunted might be what you're looking for:

http://www.tesnexus.com/downloads/file.php?id=33089

Damn, you need Shivering Isles for that!

Can you suggest a mod like that that doesn't require Shivering Isles?

I've got just the thing for you; http://www.tesnexus.com/downloads/file.php?id=5902, don't forget to download http://www.tesnexus.com/downloads/file.php?id=6226

Lost Sword of the Ayleid would be another mod like that.

As far as riddles and little hand holding goes:
Blood and Mud
And
Ivellon
do that pretty well.

If it wasn't for that no shivering isles thing I would say Integration too... some of it's riddles are really hard, and sometimes the things you have to think about aren't even riddles. For instance in one quest if you just assume and don't use common sense you might spend 2 hours dungeon crawling just because a character suggested it.