He wrote several books (but you knew that).
D&D exists in large part because of what he wrote, not the other way around. He wrote what he wrote because he wanted to create a modern myth for the English-speaking world, an ambition which he succeeded in.
As for language and the shape of the words, the tone of LotR is unique, and distinctly different from The Hobbit or even The Silmarillion. There is beauty and timelessness in the prose that many editors would just not allow for these days.
Few have been able to even come near what he did in creating his system of names, places, and world building. Tolkien’s work is the high bar against which all other world building is measured.
Even if he’d only written Lord of the Rings, at 579K words, it’s roughly equivalent to 6 or 7 full-length novels. Being an author wasn’t his primary job, he was a linguist by training. But he certainly was a “real author” as we have his books to prove it.
So troll successful, I guess.
Unpopular opinion: The Bible. Seriously. Actually reading it puts you a step ahead of most so-called religious people. You get to see how wide-spread the influences of the book are. All of sudden myriads of references and off-hand phrases, metaphors, and literary echoes become clear.
Something easier? Zen and the Art of Motorcycle Maintenance: It walks you through a discussion of Socrates, Plato, and Aristotle, and then a revolt against Aristotelian Subject/Object division, while on a cross-country motorcycle trip.
Just freaking good: Truman by David McCullough, Texas by James Michener.