written stuff I found unbelievably boring.
Jacqueline Carey wrote the Kushiel's Legacy series which I love...but she also wrote The Sundering which is absolutely ponderous. The story is basically Lord of the Rings from the POV of the "evil" side, so perhaps she was trying to mimic Tolkien's style, but it was a chore to get through those. I loved the concept, but not the writing.
Given the above, I guess I should say Tolkien. I honestly like the LOTR movies better than the books - really the only films that hold that distinction for me. I have read the series through, and I'd like to know more about Middle-earth, but the idea of picking up The Silmarillion or The Children of Hurin makes me cringe.
Robin Hobb wrote an eleven book series (3 trilogies and one 2-part)...out of that, I adore one of the trilogies and found the rest decent. But she wrote an unrelated trilogy called Soldier's Son that is just AWFUL, and centers on the least likeable main character ever.
Brust is another one where I loved the concept but not the writing. His To Reign in Hell is about the "fall of the angels", told from multiple perspectives, and is a fascinating concept. But the actual story itself dragged on terribly. It made me reluctant to try anything else of his, though in light of my experiences with Carey and Hobb, maybe I should reconsider.
(And I love A Song of Ice and Fire, but even I found the most recent one just a bit boring! I was thinking, "Come on, man! This is the best you've got after taking six years to write the thing?" )