I’ve long maintained that one of the best things about AD&D 1st edition is its modularity (and it should be noted that most of what I’m about to say also, or even especially, applies to the original D&D booklets — 0E — as well). While there’s a coherent feel across the whole thing, it’s not the case that there is any overriding universal mechanic (as we saw in versions 3 and later) that is used to determine just about everything. There are, in fact, a myriad of micro-games within the larger AD&D game, and therein, I think, lies its strength and enduring appeal.
Flexibility is the hallmark of this modular approach to the AD&D rules. It makes it possible for the DM to tinker with, or outright replace, any of the various sub-games within it, while still being able to retain the overall feel and flow of the whole and still have it called Dungeons & Dragons.
Take, for instance, the combat system. Almost since the inception of the game, different people have proffered alternative combat systems, usually on the side of adding additional realism. The modularity of the rules enables the DM to swap out portions of the combat system, or even the whole thing, and still have the whole function fine. I remember myself, when the ground-breaking Arms Law and Claw Law from Iron Crown Enterprises first burst on the scene, with their enormously detailed critical hit tables, that using them in lieu of the original AD&D combat system was all the rage for a year or so. Alternative combat systems were found in early issues of The Strategic Review and The Dragon. Unofficial supplements like the Arduin Grimoire added their own bits and pieces, and yet it was all still “D&D”.
The magic system was no more immune to change and modification than the combat system, and again the fact that it was its own, stand-alone sub-system within the rules was a hugely enabling force for doing so. Spell points were (and still are) all the rage when it comes to replacing the “Vancian” spell memorization system of AD&D and its cousins older and newer. And again they could be incorporated into the whole without breaking the whole (necessarily, that is; modularity doesn’t ensure that every replacement module is actually going to be good!). Take away spell slots and memorizing, and replace it with spell points and refreshing, or casting spells out of books, or just being able to cast any spell at any time, and the whole thing still can function in a mechanical sense. It’s still D&D.
But I would argue there are many other mini-games contained within AD&D that aren’t necessarily recognized as such. One of the hallmarks of such a thing is the fact that it’s something the player can do without the DM necessarily being involved, other than to give a cursory inspection and nod of approval.
I submit that the much-derided encumbrance system is exactly one such mini-game. Although I will agree that not every gamer found it as engaging as I did, I remember spending hours pouring over the encumbrance tables between games, figuring out how many small belt pouches and large sacks I needed to carry everything, and making sure everything was placed and balanced correctly. It certainly helped once TSR finally published official carrying capacities for such things in the AD&D Player Character Record Sheets, as a quickie table, easily overlooked, in the accompanying text on the inside cover of the booklet. Figuring all that stuff out was a game unto itself. A mini-game, if you will.
Spell research is another mini-game, albeit one that is much more dependent on the DM, who is on the hook for determining the spell level of the new spell. So too is the recruitment of henchmen; there is a whole series of steps and accompanying tables for figuring out how to find a henchman. You can post notices, hire criers, and more. The henchmen who answer your inquiries all need to be developed, and of course there’s a maximum number per settlement that needs to be worked out.
Wilderness exploration is yet another mini-game. There’s the usual bits of terrain and random encounters, but there are also strongholds with inhabitants, chances of getting lost, and NPC adventuring parties to consider. Step up to the next level and there’s clearing wilderness terrain and attracting colonists, who have a chance to revolt depending on the tax rate. There are games within games here, any one or three of which could be swapped out with something homebrewed or from some magazine or third-party product, and yet it’s still all D&D.
This approach also allows the addition of new sub-systems to cover any of a vast number of special instances that are not otherwise covered by the rules. Just look at the early Judges Guild supplements, especially the Ready Ref Sheets and some of the City-State material. You’ll see beefed up rules for encounters, rules on how to make friends with NPCs, commerce, and even large-scale warfare using hex-and-counter wargames (featuring a spearman riding a triceratops no less!). The Arduin Grimoire, already mentioned, does the same in spades, and eventually grew large enough to become its own game system. And because of the modularity of the original rules, it all can work, more or less, and it still all feels like D&D.
I feel like the universal systems that have come to dominate RPG mechanics lose this modularity, and in so doing they lose a vital opportunity for the DM to alter and otherwise fine-tune his game to suit his needs. In 1E, you could literally swap out the combat system with something from another game and keep playing like nothing happened. In 5E? That’s a much more difficult thing to do mechanically, because all of the mechanics are so interwoven. While it makes a tighter game to be sure, I’m not entirely convinced that the loss of the opportunities for innovation is necessarily a good thing.