It's main value back in the day was basically 'Holy crap! Look at all these monsters!' and 'Wow! They do games in hardback now?!' The Players Handbook is good not great. If I had to pick a single 1st edition monster book to use for all future gaming this would rank 4th or 5th on the list with the Fiend Folio at the top. The DMG is the reason why I'm so excited about the forthcoming AD&D1 reprints from WotC.
Comparing the 1st edition DMG to the lackluster 2nd edition version really shows the difference between a competent game designer and an actual ludo-genius like Gygax. I have yet to run a fantasy campaign without opening this baby up at least once, no matter what rules I use.
Not only is the classic Gygaxian prose in full effect, but it's just full of stuff that you can use in any fantasy game, not just D&D: random NPC personalities, gem types, herbs, random dungeon charts, siege engines, castleworks, government types, noble titles, gambling methods, crazy mofo artifacts, ships, potion ingredients, etc., etc.
It's the only RPG book I read from cover-to-cover every two or three years. Like it says in the title, the first edition Dungeon Masters Guide is the first thing you ought to read. In the comments to yesterday's Gameblog post Hartful asks 'What would you recommend must reads from old editions as a DM?'
