Love LoTR's as I do, the Silmarillion is indefensibley boring - real keep returning to the top of the page and keep trying not to nod off stuff. I was stuck on a bus in the outback for 3 days sheer boredom and even then I couldn't finish it. I starred at sand instead.
Know you meant 'good' but there's fifty shades of grey 'sales', more of a fad and curiosity in 1 summer. And then there's LoTR 'good' sales which still dwarf (see what I did there) popular pulp fiction books like the above example, and took decades to write such is the enormity that it defined...
Don't get all the criticism of LoTR - it's widely recognised as one of the greatest books written with hundreds of millions of fans and sales toboot. It might not be your cuppa but that doesn't make it tedious. Just you're not exactly target audience. I wouldn't try reading many of the classics...