(Digression: I guess I was "OSR before the OSR" because I never liked any of the later versions they came out with, I stuck to that 1984 release for as long as I could. Of course eventually everybody else I played with switched so I had to as well. But much to my credit I never actually bought any of those "modernized" versions, I just played them with my friends. I wish I had been just as strong when AD&D 2e came out.)
In any case, I always thought it would be interesting to share how that system worked with the rest of the OSR community, so I had planned to write a summary of the original 1984 rules in English. But I don't have to do that anymore because someone else already did, I just never knew about it until today!
I highly recommend that you read at least the sections on character creation and combat, those give a pretty good flavor; the magic section is fun too of course but less essential. The most fundamental differences to D&D are probably these:
- Ability scores start between 8 and 13; on gaining a level, a character can raise one of their ability scores by 1 up to a maximum of 20; ability scores are used for "skills" by rolling under with a d20; "courage" is actually an ability score (so player characters will sometimes run away even if their player doesn't want them to).
- Combat has no "static defenses" so both combatants roll: the attacker rolls to hit (d20 under their "attack" value), the defender rolls to parry (d20 under their "parry" value); a successful parry can result in one or both weapons breaking; armor reduces damage unless the attack was a critical hit; critical hits or missile weapons cannot be parried.
- Magic uses a "spell point" system with some effects depending on how many "spell points" the caster has left; the player has to actually recite the proper words by heart, no cheating; there are no saving throws, but the caster may have to overcome the target's "monster level" with a custom roll depending on the spell.