GOT had a very strong fanbase for 15 years before the TV show. The show took it to a far wider audience, a lot of who then discovered the books.
As far as I'm aware the Sopranos didn't have the same initial fanbase or feedback into a book culture.
I'd suspect that people will still remember game of thrones in 20 years time and be discovering the books. As such I imagine the theme will have legs in the same way that TZ, Addams etc do.
The hobbit will also be remembered but I suspect for the book rather than the films. Maybe LOTR will be for both?
A Song of Ice and Fire (which is the book series) is massive and only eclipsed by Harry Potter in modern fantasy. HP though is fundamentally a childrens story. ASOIAF (GOT) is far closer to say Shogun