Differences between Ramiel & Uriel

While the sister worlds of Uriel and Ramiel are very similar to one another, there are key differences that have arisen out of my (DrFalchion) and ManOCeltica's interpretations of the world idea that he originally began building. Please note that he and I came to the solution of sister worlds in the first place only to respect each others freedom as DMs.
There may also be other worlds in this multiverse - which would also be named after major angels - but that's a topic for another time.
Just as one example, halflings are far more prevalent in Ramiel than in Uriel, but that's not the only thing you should know...

Major Timeline Differences:

Note: You can view the 'Master' Timeline (by age/era, only world reshaping events) here

The Illithids

While it is not fully established what role the Illithids have to play in Uriel, it is likely safe to say that it is not on the same scale as it was in Ramiel. Ramiel's Mind Flayers remain quite true to the Forgotten Realms: they at one point controlled most of the astral sea (though this has different implications here, of course), and they seem to have been intruders from an unknown plane, a different timeline, or even another world (in this case, though, it's likely not Glyth, as there are only a few specific locations from that setting in Uriel/Ramiel's universes, such as Mechanus). Like in the Forgotten Realms, they once enslaved the Gith, before being driven by them to the Underdark. However, the roles they've played in the world's history beyond that are in some ways quite different, largely due to how different the timelines are.
From here on there are spoilers. Major ones. You have been warned.

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In Ramiel, the Mind Flayers' impact stretches all the way back to the first age. They brought with them not only their psionics but also powerful magic, bringing a power far beyond anything known at the time - though they were still matched by the equally mysterious Aboleths and outmatched by the gods themselves. Had they ever found the material plane at this point, its human population would have likely been wiped out or enslaved, but they did stumble upon and devastate the island of the Gith.
The Illithids were the unchallenged masters of the Astral Sea - their powers protecting them from all its many threats - from their arrival, all the way through the second age. However, as the third age dawned, the Material Plane was not the only place that the gods warred. The Holy Wars stretched into the Astral Sea, the Gith turning to divine magic to drive their subjugators away.
With much of their leadership quickly wiped out, the Mind Flayers knew they had been beaten. Before they could be killed, the remaining leaders of the Illithids tore down their empire's massive arsenals of magical artifacts - ones they had brought with them, ones they had created, and ones they had taken from others - and either destroyed them or threw them to the sea. What few Ulitharids could escape death were driven to the Underdark, eventually leading to the role they now hold as of the Fourth Age, which also matches their traditional D&D depiction.
The Illithids' leader - their Grand Cerebremancer - wielded their most powerful artifacts. The power afforded by them was enough to truly challenge the gods - in a way, their leaders ascended to godhood themselves by their power - and in the final battle, it was believed that their leader slew several of the gods the Gith had called upon, before finally being silenced by the hand of the supreme god of Law, Tsav, himself (likely for violating the natural order in doing so).
The modern Illithids refer to the four artifacts their leaders once wielded as the Primordial Shadows, and the Elder Brains retrieved just one of them - the Primordial Helm. The Helm is hardly ever wielded, for sake of keeping it secret, but if wielded by an Ulitharid it would on its own increase the precision of their psionic control by several times. The Primordial Cuffs were taken by the Gith - and its ability to grant and multiply the power of psionic abilities led to the formation of the Githzerai. The other two shadows have been long lost, likely dropped into the illogical, twisted "waters" of the Astral Sea.