In my experience the criticisms come from multiple directions, sometimes ones that contradict each other.
The word Oriental in the title.
A term that has only recently fallen from the social lexicon when describing that region of the world. It was still considered appropriate in the 1980s and only had mild pushback in the early 2000s. Regardless, WotC hasn't been keen on reusing any names of previous books save the Core, so I'd wager any new book is safe from that term.
It is Japan focused and not all East Asia.
It applies Japanese stuff to other East Asian fantasy analogues.
This is like saying "D&D is focused on Medieval England but has elements of other European cultures". Yes, the original OA leaned a little heavy on Japan, but at the time Japan had far more cultural exchange with the west than China, Korea and the like: the "War on Communism" was happening in the 80's and Japan was viewed as a good little capitalist ally. By the time 3e came around, they specifically used a popular Japanese-inspired setting with support for legacy OA elements.
It is not historically and culturally accurate enough.
It is too historically and culturally focused and not fantasy enough.
D&D isn't a history lesson. D&D assumes a world that is vaguely Medieval, but features Rennaissance-level technology, Age of Exploration-level social movement, and pre-Christian Paganism. It assumed a gladiator, a Caribbean pirate, a Celtic Druid and a Viking Berserker can all form an adventuring party.
As to the second, I cannot take seriously that either OA isn't fantasy enough.
It focuses on tropes from old samurai and kung fu movies.
It feeds into tropes about East Asians.
Yup. That was what was popular in 1980. Kurosawa and Bruce Lee was what Westerners expected of an Asian setting. Come 3e, things had move to incorporate more elements imported from Eastern culture like Anime and Wuxia.
But guess what? D&D focuses on tropes from western pop culture. Eberron is built around pulp and noir, Ravenloft gothic horror. Part of genre is genre tropes.
It is not integrated into normal D&D but is a separate elsewhere/other in both setting and mechanics.
It shoehorns D&Disms onto Asian fantasy concepts.
1e OA attempted to create an "alternative" D&D that was separate but compatible. By 3e, they learned thier lesson and nearly all the mechanics for it were in line with the d20 norms. As for separation, it IS a different region of the world, not just a kingdom you dump anywhere. Regardless, Kara-Tur was firmly established in Faerun and can be accessed by foot, steed, or spell, while Rokugan was a separate setting akin to Theros and Ravnica.
As for shoehorning D&Disms, ITS $#@&ing D&D! Of course it's going shoehorn the game into the setting. This is like getting upset that Ravenloft "shoehorns D&Dism into horror concepts" It's for playing D&D with horror tropes or playing D&D in an Asian setting.
By this logic, the only way to play different genres is to create whole new game systems to accommodate them.
It is not a broad toolkit but has specific assumptions.
So, it's a setting, like how AD&D 1e assumed specific assumptions based around the Greyhawk setting. 3e OA specifically WAS a toolkit however, presenting Rokugan as the default assumption but providing lots of things that weren't based out of Legend of the Five Rings and even gave a quick "1 page" description of how you could assemble parts of it to create a SE Asian-inspired setting. 3e OA gives you two unique examples and plenty of parts to make your own.
But sure, it wasn't a toolkit.
It is cultural appropriation.
It does not provide enough cultural representation.
It is cultural misrepresentation.
D&D has co-opted the Celtic druid and banshee, Norse giants, dozens of Greek monsters, Egyptian mummies, Romanian vampires, the whole pantheons of the Celts, Norse, Egyptian and Greek myths, Arabian genies, Japanese oni, Indian raksasha, and the Shaolin monk and crammed all of that into a boiling soup of a setting called "Core D&D". D&D doesn't appropriate culture, it mugs cultures in dark allys and roots through their pockets for spare mythology. It frequently has gotten things wrong (Hello Druids) and let that fester for decades. It's what D&D does.
1e OA made some mistakes. 3e was an improvement but could do better. But many of these criticisms strike the core of what a setting in D&D is, and they could equally be applied to most any setting or genre book.
EDIT: I want to make clear this isn't directly aimed at Voadam, but at the criticisms that were levied at OA.
