One consequence of this depth is a fractured fandom. Factions of fans occur for all fiction, but to different extents. A group of people who like the Pirates of the Caribbean movies are generally in the same boat; the media they appreciate is distinctly movie (disregarding those who argue that the ride is better and they don't watch the movies so as not to ruin the ride). Harry Potter fans may compare and disagree about both books and movies, but I feel that Lord of the Rings fandom is even more layered than that.
I went to a meeting of the Tolkien society today and in conversations about Lord of the Rings, a few careful questions calculated the level of another fan's fanaticism.
Did you watch the movies? Extended edition? Multiple times? ... to shreds, you say?
Did you read the books? And The Hobbit? Do you actually read the songs and landscape descriptions?
Have you read The Silmarillion? How about Tolkien's other work?
Do you actually think Tom Bombadil's poetry is good?
Can you read Elvish? All three major dialects? Can you speak and write Elvish?
The ability to write flowing Sindarin poetry is about the peak of fan dedication, and it's telling that the final fan milestone is languages, the very basis of Tolkien's work. I probably fit in this scale right after reading The Silmarillion and just before enjoying the Tom Bombadil poetry.