A very thought-inspiring post by Tony over at Microdungeons (http://www.microdungeons.com/), about the role of the DM in being "The Eyes and Ears of the Player Characters."
As he says:
It's crucial to engaging the players and winning their buy-in to the game. If the players can't see and hear the dungeon clearly, they can't live in it or have adventures in it. The players also have a job here, which is to ask questions for the game master to answer. A lot of people equate being the eyes and ears with providing description of the dungeon and the things in it with a certain level of gleeful embellishment. This is part of it, but there's more to 'eyes and ears' than a judicious use of adverbs. it's at least equally important to be crystal clear and fair about how what they're seeing and hearing intersects with the mechanics of the game you're playing.
DM as Storyteller
As DM, you have to be fair to the players, giving them a concise description of important information. As their "eyes and ears", you need to give them all relevant information that they would normally be expected to notice, especially anything that would stand out as dangerous or unusual. It is up to the players to "investigate the scene" further if they want to find things that are not immediately obvious. In other words, it is up to them to ask questions and guide their characters through the imaginary world.
This is the task of the DM as Storyteller. Set up cool and engaging scenarios for your players to interact with. Its all about fun, excitement, drama, intrigue, mystery, silliness, humor, and overall good times.
DM as Master of the Dungeon -- the Monster Player
Usually the DM handles refereeing, storytelling, and controlling the monsters. HOWEVER.... We can imagine a gaming table in which the Referee and the "Monster player" were TWO SEPARATE PEOPLE. Imagine one person setting the scene, adjudicating the action and rolling the dice (the Referee), and the other person roleplaying the monsters (the Dungeon Master)!
Such a split in roles might really spice up the action and drama, and would certainly help prevent the players from feeling like they were being screwed by the referee, who does seem a bit omnipotent when we consider that he controls both the MONSTERS and the RULES. As Tony puts it, players should feel "confident that the system and the game master aren't using underhanded techniques to trip them up." If the DM is a different guy than the Ref, there would be no conflict of interests.
Imagine if it was the Dungeon Master's job to take the title literally, to act as the Master of the Dungeon. Meaning, he was in charge of roleplaying the monsters of the dungeon. In other words, imagine allowing the DM to play a completely adversarial role to the players, without any refereeing duties. This DM would "play" the monsters in any encounter. That would be pretty cool even if the monsters were all just random chaotics arrayed will-nilly.
But even cooler, imagine the monsters were lawfuls, loosely knit together for some common purpose, or even tightly knit together in some command structure. The DM could have a great deal of fun playing the "boss monster". His job would be to use all of his resources and powers to thwart the PCs, arraying his sub-monsters in a planned defense, giving them specific orders. Heck, the referee could even treat the sub-monsters like NPCs of the Dungeon Master, rolling for loyalty checks and that kind of thing, to see if they followed the DM's orders properly.
So, say you have five players at your table. Instead of having each of them play a PC and you play the monsters, have four of them play PCs, and one of them play the monsters!
DM as Referee
A good DM encourages creative play by assigning reasonable chances to whatever crazy scheme the players come up with. Heroic feats should be up to the players imagination to define. For example:
DM: "Wait, what? You want to throw the gnome onto the dragon's back?", PC:"Yeah! I'll spin him around for momentum, you know, like a hammer toss!", DM:"Uh, ok, I'll give you a 50% chance of chucking the gnome onto the dragon. But then he'll have to make a DEX check to hang on, ok?" PC: "Aright, let's roll!"
Also, it is appropriate to a "real life" description to describe things in percentages and chances. For example, you could describe the cliff face: "It is a pretty steep cliff face, somewhat crumbly. You'd have about a 33% chance of falling if you freeclimbed it."
That is exactly how our minds work in real life. We take risks based on our calculations of success, based on our observation and analysis. We are generally aware of our own capabilities, so we can make reasonable deductions about our chances of success.