At the height of RPG's popularity in the early 80's one element of Tolkien's Style stood out above all else.
The appendixes for the Return of the King.
From the Greyhawk Folio to latest Forgotten Realm Hardback. From Wizard to well just about any RPG company. The appendix of the Return of the King was the ur-document on how to present a setting. After Shannara this format dominated the alternative formats notably Judge's Guild Wilderlands and GDW's Traveller.
As a 13 year old gamer in the late 70's Tolkien was the only source I had for writing up a campaign world. With King Lists and Timelines galore. However Tolkien has some major weakness as a source for RPG campaigns. Only a dozen or so elements made for good additions to a D&D game.
It the same problem that drove me from Greyhawk to the Wilderlands. The howling emptiness of the map. While Tolkien had a wealth of details in the appendixes, only a few areas were detailed enough to run an RPG campaign in: Bree, the Shire, Rohan, etc.
Myself and I am sure others turned to other sources to plug in the gaps and after Shannara there plenty to be found for whatever taste of fantasy the group preferred. One thing I learned that the format of Bob Bledsaw's Wilderlands and Marc Miller's Traveller was way better for running a campaign then Tolkien style.