No more kitchen sinks!

 I'm running a campaign set in a mythic fantasy version of the British Isles, circa 860 AD. Due to the nature of the setting, there's many monsters and magic items that are restricted from use, and I absolutely love the effect that has in game. Given that I'm using a twist on a real world setting, the players immediately relate to it and have ideas of what can and should be done in the adventure, and by limiting monsters and items, I'm able to reinforce their suspension of disbelief.
  I think that adding too many elements from outside influences such as Tolkein's works, Conan and pulp adventure stories, etc., tends to shatter disbelief and revert players into a headspace where they know that they're just playing a game. Actually one of the issues running B2: Keep on the Borderlands is the baggage that creatures like Orcs and goblins bring, because they've been done so many times in so many other kinds of games.
  In fact one of my drives to play systems like Original D&D was its restrictions on player classes and races, and a lot of my advice for running spellcasters is to limit the specific spells that they have access to. I just didn't realize that it's better to limit all of these from a setting perspective and not a system one. That might explain the popularity of settings like Dark Sun and Ravenloft, which specialize D&D in their own ways.
  Rather than running a generic fantasy kitchen sink, I think its better to see the monster manual and spell lists as options that you must remove pieces of in order to fit your campaign. Most tables that I've seen just assume that everything that exists in the rule books also exists somewhere in the campaign world, but by creating a campaign world where some things cannot exist has conversely freed me up to run a more satisfying game.

Also as a side effect, using a map of historical Britain and Scandinavia has absolutely crashed my interest in fantasy maps. Fantasy maps are usually just pastiches of real world places anyway, with odd geography. I think it would be fun to run a campaign in Central or Eastern Europe as well, which would give access to most kinds of biomes.

No more fodder enemies!

 Orcs, goblins, kobolds, gnolls, etc. are boring! They only exist as sacks of XP and random loot for players to slay in sequence. I think it takes away from the mystery and magic of a monster encounter when the monsters are so commonplace. I'm starting to prefer the approach of LotFP and other OSR games where monsters are unique and rare. Coupled with my idea of dungeons as real places, I envision dungeons that are lairs of single monsters, who are powerful and highly dangerous, but hoard massive amounts of treasure. A single dungeon, maybe 5-10 rooms, would be a cache of thousands of gold, but also the dwelling place of a small band of 3HD+ monsters. 

I realize that this is how the Moathouse in module T1 works. Most of the creatures in the upper levels are natural animals that have become giant sized - frogs, lizards, snakes, spiders and ticks. It is also a hideout for some random bandits. The lower level of the Moathouse is the lair of a single Ogre, who has his run of several rooms, and keeps prisoners locked in his pantry. It is then connected to the hidden underground lair of Lareth and his band from the Temple, and their bugbear slaves. The monster ecology of the Moathouse is very different from the Caves of Chaos, which has many diverse fodder monsters filling up the place.

I was reading up some Eastern European folk tales in an attempt to incorporate them into my adventures, and I noticed how the boogeymen in them were individuals that were highly lethal. I certainly couldn't imagine them living in groups and forming their own communities. I think monsters like that are better for an adventure, as the local peasants would be asking heroes to travel to the dark and scary parts of their land to face off against the cannabilistic hill troll, rather than asking the heroes to be goblin exterminators.

magic weapons in my campaign setting

 A +1 bonus on a d20 isn't that big of an effect. For that reason, I consider mundane weapons of high quality, like "Masterwork" or "Exotic" weapons, to grant a +1 bonus to THAC0 and damage. I'm also okay with them striking monsters that are otherwise immune to mundane damage. 

Magic weapons glow with aetherial power and grant a +2 bonus to hit and damage. Some weapons only have magical power in special circumstances, such as when used against orcs or goblins, or when held by a character of the necessary alignment. 

"Double magic" weapons glow with even more brilliant power, and grant a +4 to hit and damage. 

"Triple magic" weapons are mythical in existence and in power. They grant +5 to hit and damage, and only unique world artifacts are ever that powerful.

Orcs as Native American expys

 I love this idea. I love it so much because it makes the campaign explicitly colonial - Orcs and goblins and the other monstrous intelligent races are just naturally existing in the land and the humans are explicitly invading and driving them off. In fact it fits in almost perfectly with the backstory to the Keep on the Borderlands, where the Keep itself is established as a foothold into the "wild, untamed" Border areas. I can think of no better parallel to the American frontier of the 1800s and the idea of "Manifest Destiny". I especially love the implicit racism it projects onto the human and demihuman races and the nuanced shades of grey it adds to the greenskin races. The orc children dilemma no longer becomes so cut and dried. Gygax's assertion that "nits make lice" becomes absolutely, categorically, 100% bigoted.

Small dungeons

I like small dungeons better than large mega dungeons of interconnected corridors. Instead, I envision a “dungeon” like the single family residence of the monster. There would be only a handful of inhabitants and all the rooms they need to live in, such as a place to sleep, a place to eat, and a place to put their stuff. I also like the idea that, should you run into a monster in the dungeon, it is the monster. 

As for dungeon ecology, I consider it more natural to link dungeons across the over world, where monsters would have their own territories and travel networks. It makes much more sense that two feuding races of monsters would be claiming overlapping territories, than living in close proximity with each other, separated only by a few hallways and doors.

Running small dungeons like this means that your map scale would have to be much more precise and smaller in scale than a 6-mile hex. Alternatively, if you use large hexes, then each hex should have multiple chances of finding a lair. Multiple small lairs actually generate more interest in wilderness travel and provide a unique element to it.

Religion in early D&D

Dungeon Modules B1 In Search of the Unknown, B2 The Keep on the Borderlands, and T1 The Village of Hommlet do not reference the pantheon of deities that were introduced in "Gods, Demigods and Heroes" or in "Deities and Demigods". Instead, there is an oblique reference to a Church and a singular religious figure, St. Cuthbert.

In B1 the only references are in the names of the pregenerated Cleric characters, one of them is a devotee of the "Great Church", another of the "Secret Church", and one of "St. Cuthbert". In B2 there is a chapel inside the Keep, the Curate who maintains it, a duplicitous priest who lives in his own house, and the Temple of Chaos, but there is no mention of which deities any of them serve. In T1, the Church of St. Cuthbert has a strong presence in town and causes tension with devotees of the town's Old Faith.

These modules give us a fragment of a glimmer to how D&D was played in its early days, and to me it seems that instead of using a strict pantheon of gods, early campaigns relied on a loose interpretation of Christianity and pagan faiths from British medieval history. I think the addition of a strict pantheon of gods to the worlds of Greyhawk or the Forgotten Realms, or any other, is a mistake and actually divorces the game from its inspiration and restricts the kind of stories you could tell. I find a looser interpretation of religion more to my taste, as something that's closer to historical reality than the mess of fictitious deities that everyone plays with. And, I think a proper implementation of religion into D&D can help explain some of the more incongruous aspects with the game, such as the cleric and paladin classes or the effect of resurrection on elves, and the lack of demihuman PC clerics.

Here's how I would remix it:
There is a Great Church in the land and its patron saint is Saint Cuthbert. (From the modules above, there is no indication that St. Cuthbert is a deity, rather than just a venerated saint.) The Church represents the totality of organized religion, and all human settlements have at least a chapel or some place of worship around which the village has grown. The Church is humanocentric, and only admits humans into its highest ranks.

The Great Church allows members of its clergy to wander the world as missionaries and enforce their mission by force of arms. These Clerics still follow precepts of the Church such as the restriction against shedding blood, and through prayer and knowledge of scripture they are able to perform miraculous works such as healing others and stopping harm to the body through disease or poison. Clerics can travel the world dressed and armed as Fighting Men, but choose to carry blunt weapons because they are trying not to kill their opponents.

The Paladins are an Order of Fighting Men who swear loyalty to the Great Church, and through their faith can perform some miracles. These men are not part of the Church hierarchy but can also heal, cure disease and are protected from evil. (Interestingly, OD&D Paladins cannot cast Cleric spells). Any deviation from their code of ethics results in an immediate loss of their powers, and they must atone and perform penance under the guidance of a Church hierarch to get it back. Only human fighting men, so devoted and charismatic, are admitted into the Order.

The language of the sacred texts of the Great Church is considered the Lawful alignment language, and it has become the de facto language for legal documents and academic documents in Universities of higher learning.

Outside of the monolithic human church, the spirits of nature and natural phenomena are worshiped by the intelligent races such as Elves and Hobbits, and even some humans are devoted to this worship they call the "Old Faith". Like everything humans do, they've created a high structure of wise men called Druids, who worship Nature and strive to keep a neutral balance among all things. Elves and Hobbits generally stay away from the circles of the druids, though some individuals may join. The language used to commune with Nature is considered the Neutral alignment language.

Hiding from open engagement with the other two is the Secret Church. This is made up of people who use the sacred texts and teachings of the Great Church and reverse its meaning. Those who speak the reversed language can cause the opposite effect of miracles to take place, such as harming instead of healing, cursing instead of blessing, and damning instead of saving. Wandering militant devotees of this Secret Church are evil Clerics, well versed in the teachings of the Great Church who must also follow its stricture of behavior, such as the ban on shedding blood, otherwise they do not have access to the miracles they wish to misuse. The reversed language is called Chaotic, and speaking it attracts demons, devils, and other fiends from the lower planes, and also grants command of evil spirits and the undead.

Apart from the main religions there are many discrete Cults and Temples, all devoted to their own deities and beliefs, who may or may not be a real creature from a higher or lower plane.

A final note about Clerics and Paladins - In AD&D certain demihumans can multiclass as fighter/clerics, such as the Half-Elf and Half-Orc from the PHB, and an expanded list including Dwarves and Elves in Unearthed Arcana, which gives them all the weapon, armor and health bonuses of the Fighter class and the spellcasting ability and saving throws of the Cleric class, thus creating a very potent combination at the cost of a halved rate of level advancement. Humans gain no such multiclass ability, and so the Paladin is the only way Humans can gain such bonuses. The Paladin generally speaking has better abilities than the Fighter/Cleric but his spellcasting is weaker, and must maintain a very high charisma and a strict adherence to Lawful Good, or lose all his abilities and be demoted to the level of a standard fighter. In this way the Fighter/Cleric has it easier, but a Paladin played well is much stronger.