So basically if you made a clone, a new edition, or even a .5 or .75 edition of D&D what would you take?
I considered this for a while as a project. There are a ton of things I've learned about rulesmithing since I ran 1e AD&D, and I've since read numerous old articles in Dragon magazine that I'd either never before encountered or didn't understand at the time which I'd want to incorporate into a rebuilt 1e AD&D.
I think I could make rules that if I sent back to my past self would utterly wow me circa 1992 or so. But the important thing to understand about my rules set in 1992 was that it was in many ways trying to be the game that 3e was. Monsters were given ability scores, constitution bonus, and so forth. Attacks of opportunity where a thing though they used a different clunkier terminology than 3e used. The concept of feats existed in a prototype form as combat maneuvers. I was evolving NWP's toward a true skill system, and so forth.
So what I realized is that my nostalgia rules would be a lot of work to produce something which was close enough to 3e that there would be little reason to not use 3e. It would be inevitably a 1e heavily influenced by 3e, clinging to older concepts largely out of nostalgia. So I never really wrote it.
Conversely, I'm exceptionally happy with my 3e homebrew rules, which I jokingly refer to as AD&D 3e or D&D 3.25. Because these rules are so close to what I ran in 1e AD&D, just cleaner, I still run 3e D&D as if I was running my 1e AD&D game. There are portions of 1e AD&D that I at various points considered importing over to 3e. The one I miss the most is the 'Weapon versus AC to-hit Modifiers', which is just absolutely beautiful in play (especially at lower levels). However, since 3e combat is already more complicated than 1e combat with more modifiers to remember and more things going on, importing the complexities from 1e that 3e lacks in practice makes combat too slow. Sadly, I've had to drop the concept, though if I was implementing the rules set on a computer for a video game, I'd definitely bring it back.
The 1e AD&D concept I'm most likely to bring back at this point is the exponentially increasing XP curve needed to level up. The 3e concept of linearly increasing XP turns out to be really difficult to deal with in play. It's forced me to adopt a custom table that reduces XP awards as you level up, where as such complex calculations might not even be necessary if costs to level increased non-linearly. It also means that you can't restart a character 1st level (or other low level) in an existing party the way you could in 1e because you never catch up the way you did in 1e. Finally, as a Simulationist, the linear increasing XP creates demographic difficulties in the campaign. The most obvious one is the problem of demihuman demographics where the demihumans in question live much longer lives than humans. If a demihuman survives 5 or 10 times as long as a human, what prevents the demihuman from obtaining 5 or 10 times as much XP? With 3e's linear XP rules, this inflates the average expected level of say an NPC elf to be a large multiple of the average expected level of an NPC human. If active humans obtain 8000 xp over the course of their lives (4th level), an elf obtaining 80000 xp would reach a 13th level. Average elderly elves being 13th level is a problem. By comparison, in 1e AD&D with its exponential XP costs, elves that earned 10 times as much XP were only two or three levels higher than their human peers, which was completely workable and interesting. Right now I'm dealing with it by saying that long lived races aren't as active as humans but I dislike this obvious kludge especially compared to the wholly internally consistent demographics of my 1e world.
I suspect over time something like the 2e Priest Sphere system is going to creep into my game, as I'm a little bit unsatisfied with the thinness of the Domain system (even as I love its elegance). I intend to do some revisions to my Champion class (variant Paladin, inspired by Green Ronin's 'Holy Warrior' in 'The Book of the Righteous'), which are going to require an expansion of the clerical Domain system and that will likely make it more like the 2e Priest Sphere system in some ways.
