The document that changed gaming forever?
The System Reference Document, including the Open Gaming License, version 1.0a
The document that got me into gaming and holds a special place in my heart?
Funny as this may sound, it's an old book called "The Winner's Guide to Board Games" - published by Playboy, of all people. It had many chapters on games from chess to risk to diplomacy... to, at the back of the book, Dungeons and Dragons. That piqued my interest (at the tender age of six) and when I was 8 years old and saw a D&D Expert Boxed Set (I started with the Expert, not the Basic set, oddly enough, because the local drugstore didn't have the Basic set), I had only one thought... "IT MUST BE MINE!" Besides, author Jon Freeman's rant at THAC0 and Armor Class rules is worth the price of admission alone. As best I can recall, it went something like this:
Armor Classes are unrealistic, illogical, and totally unrelated to the number needed to hit them. Why don't the numbers go up? In D&D you have the silly spectacle of adding a +3 shield to a fighter in plate mail and a shield (AC 2) and getting a resultant armor class of -1. Yup, 3 + 2 = -1. Makes you wonder how they got out of high school algebra, doesn't it? TSR's response to such incongruities is, "you'll get used to it." You can get used to anything, even withholding taxes, but that doesn't excuse what seems to be at best a lack of imagination or at worst sheer laziness.
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Others may be confused by the different concepts of "level" - a 5th level wizard, who is limited to casting 3rd level spells, might be attacked by a 4th level monster on the 6th level of the dungeon"
I know I didn't get the quotes exactly right, but they're close. I find it amusing that when the book was written (1975), the whole THAC0/Armor Class thing was getting panned... and only it only took 25 years for a change to be made. LOL!
All five boxed sets (Basic, Expert, Companion, Master, Immortal) hold a special place in my heart, but even those, I don't think, had quite the impact on me that the SRD/OGL did. They captivated my imagination as a youth... the SRD/OGL got me as an adult... and between you and me, that is saying somthing.
--The Sigil