I am no expert on the industry, but I gather than the 1e Oriental Adventures never made that much of an impact. I remember buying it when I was 12 or so, and being excited by the possibilities (I mean, playing a NINJA or a SAMURAI, dude, sweet!!!).
Getting into it, I think we were a bit put off due to all the foreign vocabulary and never really used much from it. I think the reason it never took off, more than anything else, was that it was designed to be its own campaign world, it was not really well suited to plug-n-play into the regular D&D world.
However, re-reading it as an adult, I am really appreciating it for its amazing creativity and thoughtfulness. I do not intend to run a "oriental-only" campaign, but I have thought of some cool ways of incorporating it into my campaign milieu.
Integration into AZ Adventures
The premise of AZ Adventures is a dawn-of-civ frontier-type scenario, in which multiple colonizing groups are converging in AZ, struggling for dominance. I had previously postulated that a group of "Asya monks" had set up a monastery nearby Sin City (see here http://oldschoolpsionics.blogspot.com/2010/12/asya-monks-of-arizona-overview.html). I am going to run with that idea and expand it further: In fact, the monks are just one aspect of another major colonizing group (the Asya) approaching from the northwest.
Aside from being an Asya population center, Sin City will be run by Yakuza gangsters clans! Reading the description of Yakuza, it is as if they were perfectly designed to run the place. The text even says Yakuza come with 3 proficiency slots, one of which is automatically GAMING. Ha!
And, yes -- NINJAS! Ninjas will definitely be part of the Sin City experience. They are basically Thief Acrobats with the ability to Assassinate, but they have to maintain secret identities, going by night as Ninjas but by day as something else. Special Ninja powers include walking on water, and, at a high level, passing through walls!
Presiding of Sin City on the "official and public" level, will be one noble clan, with the family leader (Daimyo) and crew of Samurai. While they function as the public face of the city, they are not, however, the true rulers of the city, which is controlled by the Yakuza clans. Lots of intrigue, plot lines, and adventure hooks to be explored there.
The Shukenja are the religious priestly-monk types, close in kind to Clerics. They have one temple in Sin City itself.
The Sohei are the warrior-priest monks, essentially like Paladins, great fighters who are able to cast cleric spells at a high level. They live with the Shukenja.
Wu-jen are powerful spell-casters, but they are more like wild shamans than civilized magic users, and they do not live in the city. Their spell abilities are like a combination of Magic User/Illusionist/Druid.
The Bushi are the low-class common fighters of the city, and the Kensai are the "sword-obsessed" martial artists. While PCs might run into a gang of bushi who would attempt to beat them up and rob them, an encounter with a Kensai would be a challenge to a one-on-one duel, like a shootout on a Wild West street....
All in all, as you can tell, Sin City would be a very fun place to adventure in.
Asya Colonizing Pressures
As a colonizing group, the Asya would be pressing in two directions: southward down the Colorodo River and eastward across Rt.666. A conflict point with the Arya would be in the river-side trade town at Blythe. Conflict with the Derjuden would be focused along the northern roads, as they Yakuza tried to move into control of the trade routes.
The Wu-jen would be naturally friendly with the shamans of the Dineh, and unfriendly towards the Druids of the Arya. Perhaps some Monmore missionaries would be present in Sin City, but not much direct contact between those groups would be evident, as they are on opposite sides of the state.
On a the Secret of Megadungeons
16 hours ago