For instance, with the fact Tolkien's world is what it is and what it was meant to be.
The tale suffers from its glorious mythical fairy-story atmosphere, which does not allow the accounts on the psychology of the characters to develop fully. But this is more of a matter of genre, and not a disadvantage sooner than a necessity. I ever admire the beauty and the tone of Quenta Silmarillion and the amazing depth of -- Siddhartha, e. g. Question of tastes, may be. But Silmarillion might be rewritten in a different way, and still relate to the same history.
Avantguardian -- You must realise that The Silmarillion, as it was published, was put together mainly by Christopher Tolkien, JRRT's son, posthumously. JRRT himself had no real say in the way in which that book was constructed, edited or published. Some things within the published Silmarillion are entirely written by Christopher Tolkien as well - the Ruin of Doriath chapter leaps out as one very prominent case of this.
"The tale suffers from its glorious mythical fairy-story atmosphere, which does not allow the accounts on the psychology of the characters to develop fully."
Tolkien, I believe, was not meaning the story to be a "psychological", developmental, allagory. It was the wonderful, 'been passed down by word of mouth and written for the first time', type of tale that embodies the triumph of good over evil. It shows the struggle against evil, and, as in reallity, some of the times when it does conquer. But good does conquer in the end, giving it a wonderful feel of fulfilment and reallity. For good will triumph in the end, no matter what.
Personally, I could ask for any more in Tolkien's writing. He is amazing, especially when it comes to his attention to detail! He created whole languages and truly developed something unique. As for me, the psychology of the characters just isn't important. The questions and gaps he leaves you with (though he manages to fill most of them) are an essential part of literature. So perhaps the gaps you see in character development are left there intentionally...Okay, I've totally confused myself!
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The more I consumath the more I hunger for, render me the Silmarils!
His place among writers? LOL - I'm sure that for Ronald it's still the "Bird and Baby". He, James, Fyodor and Hermann sit around together over beer and talk about anything but religion, psychology and philosophy, more than likely. As far as anyone can predict, each has a solid place in history, and even were their works comparable those places can't be traded like poker chips. Perhaps if you framed a more specific question you'd get a more satisfying answer than "Tolkien rocks, dude!"