One innovation per edition

[fuindordm]

The healing system being proportional to each character and limited by a per-character resource (surges), so for the first time non-combat classes like mages didn't recover from injury faster than combat classes like fighters

True, I forgot that one. It doesn't quite fit into an 1e/2e style game but introducing healing surges (and later hit dice) as a player-controlled, mundane resource was brilliant.

5e could have run with the concept and done something really interesting with hit dice, by making them a balancing factor for powerful spells and other magic, or allowing PCs to use them for other things like feats of adrenaline.

 

[PHATsakk43]

While it’s probably forgotten now, but 2E initiative was the best the game has ever had. Roll low mechanic is the best for initiative. 1E was so bad in comparison.

THAC0 has been suggested for 2E but BECMI and I think B/X had it, both of which came first.

5E has to be advantage/disadvantage

 

[The Sigil]

1e - base rules for campaign
2e - incentives for single-class PCs (specialty priests, specialist wizards, weapon specialization for fighters...)
3e - feats, so that players have some leeway to customize their base class
4e - a warlord base class
5e - class/subclass structure

As I'm writing these, I realize that they are all on the player side. Frankly, I can't think of any major innovations in the rules that really transformed the game for me as a DM. Advantage/disadvantage is useful but doesn't quite meet the "gotta have it" threshold. 3e-style magic item creation is a mixed blessing and more for the players than the DM.

How about you all? Are there any rules or quirks from earlier editions that you now consider essential, no matter what edition you're playing?

• 1e - Initiative Rules - declaration of intent before actions are resolved... which means Weapon Speed and Casting times for spells affect your initiative roll (EDIT: and yes, "roll low is good" but it does kind of conflict with my 3e choice of the d20 mechanic where higher is always better) - Weapon Speed and Casting Times actually gave you a mechanical reason to use lighter weapons or lower level spells since those resolved faster!
• 2e - Skill/NWP/Ability score checks ("roll under ability score") - makes the 3-18 spread make sense instead of the modern game where ability scores are really "-1 to +4"
• 3e - This is a hard one; the core d20 mechanic, but that includes ascending AC. Probably the Fortitude/Reflex/Will division among saves would be my second choice. (This one also goes against the best things I am pulling from 1e and 2e which are "roll under" mechanics). Honorable mention: Metamagic Feats.
• 4e - This will probably be unpopular, but abstraction of powers to "at will", "encounter" and "daily" (kind of match up with 5e's "unlimited cantrips", "once per short rest" and "once per long rest")
• 5e - Advantage/Disadvantage (which is much easier to track than 3e's stacking/overlapping bonus system where you had to pay attention to the "type" of bonus). Honorable mention: Upcasting/heightened spells (which I thought was a brilliant solution to 3e's geometric wizard problem).
• BECMI: The Companion Set's Dominion and War Machine rules (I consider those both to be part of the "Domain" rules though some might separate them)