What do you like to see in the text description for a monster?
I think the 1e MM had it just about right. You get a summary of the monster's appearance, organization, habitat, weaponry, and modus operandi, and not much more. When I write descriptive text for a monster, I try not to write more than a GM could read in 60 seconds.
Here's my entry for "Goblin" in the DungeonTeller RPG:
Goblins are malicious, unruly, underground folk. They live in bands of 20 to 200 individuals, occupying a central, well-hidden cave and any number of surrounding mining tunnels. For every 10 goblins, one will be a “boss” who acts as an overseer. The bosses, in turn, report to the band’s king or queen. Occasionally a successful king or queen will rule over several bands. Each band also has its own hobgoblin wizard – it’s a rare goblin who can cast magic spells! (Hobgoblins receive their own entry in this book). Goblins mine metal ores as well as the coal they need to smelt the ores. They also raid dwarf mines for cartloads of ore and for prisoners they can use as slaves. When the ore in one area is exhausted, after a period of years or decades, the goblin band will move on to new grounds, leaving their cave and tunnels behind, often to become occupied by other underground monsters. Much of the underworld was carved out in this manner, making goblins an important part of the deep ecosystem and economy.
Goblins typically carry hammers and picks scaled to their size, and a bag of stones for shooting at enemies with a slingshot. They love cacophonous music, and sometimes throw wild revels accompanied by banging drums, rattles, and horns. These revels can be heard for miles underground and are sometimes the first sign that a goblin band is near. On the prowl, however, goblins are extremely stealthy and like to surprise their enemies with overwhelming force in terrain that favors their position.
In the 2e Monstrous Manual and certainly by the 3e MM, the descriptions became longer and more technical, two qualities that I find toxic to my sense of wonder. As one of my professors often said, "Evoke, don't describe." I like to leave enough unsaid so that I'm not imposing my goblins on your game. I think this principle may also illuminate why David Sutherland was perhaps the ideal illustrator for D&D. When I see a Sutherland illustration, especially, I feel I'm looking at an adventurer's impression of a monster, rather than a literal depiction of it, like something a PC might sketch out on a napkin in the tavern after returning from the dungeon.