Introduction to the setting:
To call M.A.R. Barker's Tékumel unique is a huge understatement. It is as richly detailed a fantasy world as Middle Earth. Drawing inspiration from cultures and mythology from Byzantium, Egypt, Tenochtitlan and India Barker crafted a world with a unique culture.
A colony world of a vast human & alien sci-fi empire was somehow thrust into a pocket dimension, thousands of years later this culture became Tekumel.
Tékumel is ancient, and its inhabitants are aware of the cyclical nature of time and the inevitability of decline. The world is dominated by five major empires, each with its own distinct culture, religion, and political system. Tékumel's pantheon is vast and diverse, with over 100 major deities and countless minor ones. The gods are not simply distant figures; they actively interact with mortals, granting blessings, demanding sacrifices, and even incarnating in the mortal world.


Role-Playing in Tékumel:
Tékumel provides a very rich and immersive setting for role-playing. The complex history, diverse cultures, and powerful deities offer endless possibilities for adventure and intrigue. Players can explore ancient ruins, navigate courtly intrigue, engage in epic battles, and interact with a dizzying pantheon of gods. The emphasis on cultural detail and realism creates a unique and challenging experience for players who are looking for something different from traditional fantasy settings.

Flaws:
The very unique culture of the setting seems to be its greatest weakness, there is a lot of cultural impedance for most modern audiences and this most likely contributed to the difficulties in book sales and the small size of the RPG following. Characters are embedded in a clan structure that constrains behaviour in ways that can be challenging to navigate for both players and GMs.


Overall Takeaways:
I can't really recommend playing in the world of Tékumel as I've not done it, but I can recommend mining it for things like characters, ruins, monsters and for creating a feeling of deep history. Additionally the clan based culture can be taken from Tekumel and used to model an ancient, unchanging & tradition-bound insular empire that your PCs can encounter as outsiders.

Personal note:
I was introduced to this world via picking up a copy of The Man of Gold from a second hand book store and falling down the Tékumel rabbit hole. Sadly, I've never played Tekumel as it's not very popular but I fell in love with the care put into the worldbuilding and feel the urge to share what I have found for younger folks like myself who may not be aware of this gem.

Resources:
https://www.tekumel.com/world.html
https://en.wikipedia.org/wiki/T%C3%A9kumel#Published_works