I think there has been a change in the years since I was at University reading Literature when and where Tolkien was very much a "love that dare not speak its name" - he only got a mention with regard to invented languages in linguistics so I am pleased but slightly amazed that so many of the younger downer seem to be getting the chance to write essays on him. And although there are some excellent works of criticism youdotn' need them to access the work (though I found Forster invaluable when I first read the Silmarillion!).
I think the literati hate that he doesn't fit into their categories and it is a particular thorn in their side because the academic credentials of the author mean they cannot easily dismiss it. And Tolkien did not so much write a novel as create a world. It is not hard to fault Tolkien as a novelist (though it was evident that many who reviewed TCOH hadn't actually read it), but the world he created is so marvellous and intriguing... I know it isn't real, I don't pretend it's real but I love the plausibility of the creation. This is what brings us back - that and the wealth of information made available us through the editorship of Christopher Tolkien. We can get so involved in it because there is so much to be involved in and that may link in to other interests we have. For I read Tolkien as the history of a created world rather than as stories - I seldom read through the books straight but use them as resources for whatever aspect I am currently interested. Tolkien in some ways is at his best with what with other writers would be trivia but with him are simply the incursion of the wider creation in to the plot.
I found Middle Earth a refuge first time round from the troubles of adolescence and second time from the pain of bereavement but it is so much more than escapism. I have over "comfort reads" (eg the Forsyte/Barchester Chronicles) but I don't spend my life discussing them online as I do Tolkien. I am a fairly omnivorous reader (though actually not much else that is "fantasy") and read both supermarket chicklit and Booker listed stuff and lots in between. I am not claiming that Tolkien is the best writer if it meant placing him above Austen or Orwell or that LOTR is the best English novel - technically Middlemarch may well be but I have never been able to face reading it a second time myself), but perhaps he is the most beloved writer and I would point out that LOTR was voted "Book of the Century" before the films came out so it can not be claimed that its popularity is distorted by people who may have seen the films rather than read the books. The only reason that Tolkien might not be my "Desert Island Discs" book choice would be the difficulty of choosing a single volume! Currently in my bag I have LOTR, Silmarillion,UT, letters and the Journeys of Frodo which I regard as a bare minimum!!!
I am ashamed to say that I stopped reading Tolkien at University (though he was the reason I was so keen on the linguistics component!) - I had exhausted the canon and found the early volumes of HoME tough going and with a lengthy reading list making demands on time and pocket and it was the publicity surrounding the films that reignited my interest - I got full marks in a quiz without having glanced at the books for the best part of a decade! And there was the internet to allow me to get in contact with like minded souls (noone in my RL is really interested). It has swallowed up more of my time than I want to think about but I don't think it wasted.
So to give a short answer after a long one, Tolkien has breadth and depth and the more you look the more you find.