[Rogue cautiously opens door after searching and finding no traps.]
DM: The door opens with a creak. The air from beyond is musty.
[DM pause for players to walk in, look through on an angle without opening the door further, etc.]
Rogue: What do we see?
Fighter: I enter.
DM: Hang on a sec, looking to Rogue, "You see a small room with rough stone walls. Dust upon the floor ... Sir Lionheart pushes past you, with the door wide open you see a low desk, the air wafts across the shreds of a crumbling parchment on the desk." Back to Fighter, "As you enter, a hooded lamp on the desk springs alight with a blue glow."
Rogue: "Errr, did I see anything in the dust?"
Fighter: "I stride across to the desk and look at the parchment."
DM: To Rogue, "The semicircle of the door swept through the dust ... the footsteps of Sir Lionheart ... hmmm some sort of rectangular patch without much dust ..."
Rogue yells, "Don't ..."
DM: To Fighter, "Anyway, you stride across the floor and look at the ancient parchment. It is in fact a thin book, opened near the middle, Elvish runes upon the pages ..." Do you read Elvish, nope, ok ...]
Rogue: "Hey, something was moved recently."
Fighter: "Oh, it appears so. This book is Elvish."
DM: "A large dusty stone block falls from the ceiling, knocking Sir Lionheart a glancing blow ... Make a Reflex save ..."
Fighter: "Reflex? Bugger. DC 12?"
DM: "No. Take 14 damage as the block bruises you, slamming you back against the desk, you manage to avoid hitting the lamp, but your armored butt lands square on the book." Looks to Rogue ...
Rogue: "Fine. I look up at the hole which the block came through."
DM: "Lilly sees a cubic hole with 2 foot sides through which the stone fell. Make a search check ..."
Rogue: "DC 30."
DM: "Yes, as you look closer you see a couple of runes at the top of the cubic indentation in the ceiling."
Fighter: "Well, I get up and look at the book."
DM: "It's damaged. What do you do with it?"
Fighter: "We'll wait for Erasmus [the Wizard] to take a look. Is there anything else?"
DM: "Ah yes, in the blue light you also see a diamond on the back of the wooden door that you opened."
Fighter: "Anything else?"
DM: "Do you guys search?"
Rogue: "Yes."
DM: "Ok, pretty quickly, you'll find the outline of an opening behind the desk. It's about 3' by 6'. Looks like someone tried to plaster it up and then make it fit in with the rest of the walls - a poor job in your opinion Lilly."
Basically, it really depends on what the characters do. My initial description is always going to be brief, unless I want to have an immediate storyline impact on them (e.g. the magnificent Taj Mahal - that would get detail

. If they start investigating in detail, then I'll start giving them detail - that detail may or may not be important ... and the manner in which they investigate will effect the outcome. e.g. If the Fighter had waited, the Rogue would have noticed the 2'x2' outline without dust as the door was opened wider.
Just my thoughts ...