Part of my dilemma and part of my delay was that I suspect many, many people will include this book (and its fellows) in their own essential reading list and it seemed a bit obvious and a little trite to have led with this.
I had read The Hobbit at an earlyish age, too young at the time for access to the adult section of my public library, yet I braved the raised eye brow of the stern library staff and found the 1970's hardcover edition of The Lord of the Rings and was enthralled. The large pull out maps, the yellowish paper and the quality of the publication - better than anything I've since owned - all combined into one of those defining moments in time.
And what I loved, and still do, isn't the extensive back story and the elvish and other languages or the detailed appendixes (though I love them all) but what enthralled me was the story. And it is the story that keeps bringing me back to The Lord of the Rings.
This first book is a journey from the comfortable and comic into the dark and the deep. It provides the linkage from the 'written for children' to the 'written for adults'. It starts a journey that took Tolkien a long time to complete and which sets the stage for one of the great tales of modern times. Enough said.