John Ronald Reuel Tolkien was a philologist who worked at the University of Leeds and the University of Oxford…and he was also a writer. Though you’re likely aware of that last bit.
Following his death, his son Christopher Tolkien started editing and releasing his unfinished writings.

I think it’s important to emphasize that he had a full-time job separate from writing.
Writing was essentially his hobby.
This is something I’m noting specifically because of comparisons to Mr. Martin.^A)

I do really admire Tolkien, though I must admit that until fairly recently I didn’t have much personal experience with his writings. However…that’s not stopping me.

I think that while his world is very intricate and detailed…whether it’s an example of good worldbuilding or not is ambiguous. For example: most of his languages don’t really exist in any ‘complete’ form. Though it’s like this because Tolkien didn’t create them with the intent of use: they were made to satisfy his aesthetic and creative tastes.
It’s kinda difficult to figure out how to explain what I’m thinking here, but I think what I mean is that what’s there is generally of a high quality…but there’s a lot missing. A lot of what’s missing can be inferred or reconstructed, but then some stuff just can’t.
There are also possible issues with things like the timeline, but I’ll leave that for the Legendarium‘s article.

I believe that Tolkien’s fatal flaw was perfectionism. Basically, instead of just writing something, releasing it and moving on…he kept rewriting the same things over and over again, with the intent of making it perfect. This was the case with The Lord of The Rings which went thru multiple drafts before it was actually released…and was especially true of The Silmarillion which went thru many more of them.
As a result, there’s a surprising amount of stuff which is never actually properly explained or dealt with…and a lot of emptiness in the Legendarium. For example: the Hobbits – who are of supreme importance to the events of the Third Age – have no known origin and never appear prior to the Third Age. How Tolkien never noticed this glaring hole is perplexing. There are more examples, but I’ll talk about that later.

At some point I’ll add a little more that isn’t Legendarium-related, once I go thru it.

• Tolkien Estate's Website