A horror movie:
You are going down a hall.
The music begins to swell...a pair of minor chords oscillate ominously.
You know what's down this hallway: The Plot.
You don't always want to do that.
We evolve--sometimes unconsciously--different ways of DMing different groups.
The most effective demeanor for dealing with my current group is: act like Bill Murray drinking coffee while trying to get his cigarette lighter to work.
Act light, act negligent, act like you can barely remember, act as if telling them what's going on is the last of several things on your mind. No lush word pictures, no candles, no mood music.
This instills a gratifying panic in the players.
Conventional wisdom is: the DM acts engaged and fired up and epic and grand, and then the players get engaged and fired up and epic and grand. Maybe this is true with some groups, not mine. They start out engaged--they want their characters to do things, and they want to make sure things don't get done to them. They have shit ready to do before I even tell them where they are. They have armor classes and memorized spells and they dream big dreams.
So they are waiting waiting waiting to see what will happen.
So you tell them...almost nothing.
"You see, like...y'know" (sip your drink,) "...like, a room. There's..."
Inevitably I get interrupted at this point. A room? The players have a whole lists of things they want need must absolutely do to this room right now.
"Hold on, hold on. There's something there..."
"What is it? How big is it? Does it have claws? Oh MY GOD WILL IT MURDER US ALL?"
"...Huh..mayyyybe...lemme roll on this chart...talk amongst yourselves for a second..."
They are wild now, asking questions, on top of each other, over each other. And they are paying waaaaaaay more attention than they would if I'd just bathed them in purple prose describing all they see in minute and mood-setting detail.
Because when faced with this, they need to ask questions, they need to observe, their characters' very survival depends on it and--this is important--even though I appear to be more concerned about getting another Oreo or cleaning a spec of something off my fingernail than I am about telling them what's in front of them, they know that I know everything they need to know.
They know I know how big it is, I know how many hit points and tentacles it has, I know whether there's a pit trap next to it, and I know whether the door opens in or opens out and I know which side the knob is on, and I know how many feet they just fell down the stairwell.
And the fact that I don't seem to care that much either way about all these things that affect their fate terrifies them.
Or at least it serves as a heads up that they'll have to be very careful. Like when you play hide-and-seek and the kid who's "it" counts but doesn't count out loud.
In the most desperate situations, they hang on my every mumbled, like, uh...Southern Californian word. They mentally translate from contemporary american english into what this means in the fantasy world that they occupy. I don't have to do it for them. Since their characters' lives are at stake, they extract special meaning from a phrase like: "It's got three eyes and the third one lights up with, like, this sort of greenish, like..."
They are terrified because it appears I don't care. I am just relating the horrible things that will happen and making the world react the way the dice tell it to and I have zero interest in letting them know whether this is the right hallway or the wrong hallway or the horrific danger hallway or if this is "meant to be" a horrific scene or a heroic scene or what. They have to figure it out all on their own. This is far scarier and far more fun than making them sit through my HP Lovecraft impression every time they get into a new room. (And that would bore them and seem cheesey to them anyway--they are imagining the stairwell in all necessary detail already because they know they need to in order to survive.)
The terror and the engagement don't come from me being Vincent Pricey or Peter Jacksony and hoping they get into it, the terror and the engagement come from the players realizing in their own minds that this or that casually dropped word might just be the thing that kills the character they have so lovingly levelled up. And they like it, because now instead of tourists, watching amazing things, they are wrestling with the things, trying to extract meaning from a barely-landmarked world.
David Foster Wallace on a similar phenomenon:
Because, of course, great short stories and great jokes have a lot in common. Both depend on what communication -theorists sometimes call "exformation," which is a certain quantity of vital information removed-from-but-evoked-by a communication in such a way as to cause a kind of explosion of associative connections within the recipient. This is probably why the effect of both short stories and jokes often feels sudden and percussive, like the venting of a long-stuck valve...Nor is it an accident that the technical achievement of great short stories is often called "compression" -- for both the pressure and the release are already inside the reader.
Further, this technique makes the game more about them than me, which is always good. I want to be like Nanny in Muppet Babies--show up, give them a new toy or rule or plot, then let them go nuts trying to figure it out.
Like I say, this works on them and they like it. Different players, you might roll with them in different ways.