Stephen King stated that Stephanie Meyer of Twilight fame is not a good writer. I've heard the same said about J.K. Rowling (Harry Potter), although Mr. King's opinion differs, as well as Dan Brown (The Da Vinci Code).
Yet, all three are touted as good storytellers. Their books and movies have certainly proven that storytelling sells. What stories they have told and can tell!
Although their storytelling abilities are strong, their writing tends to be clunky, disconnected, rambling, etc. (Enjoyed the movies based on all of the above author's books, but did not enjoy the reading experience of their books at all.)
Dean Koontz's mastery of words, grammar, etc., is strong; however, his ability as a storyteller lags at times, devolving into rambling narrative and rushed lackluster endings. Thus, in my humble opinion, Mr. Koontz is a good writer, yet not a good storyteller. (Enjoy the reading experience, but am not always satisfied with the development of the stories or the endings.)
While Sherrilyn Kenyon has bouts and spurts of good writing in her books, her ability as a storyteller has suffered greatly over the years. Although it's debatable, I would personally consider Ms. Kenyon a better writer than storyteller. (Enjoyed very much her earlier books, but am no longer a reader or a fan.)
By most standards, the likes of Stephen King and Nora Roberts are considered masterful writers, as well as great storytellers. (I can stay lost in the worlds and characters each create for hours, and the depth and power of the experience stays with me long after the books have been read.)
As writers, we may tend toward having natural abilities with either writing or storytelling; however, a balance and strength in both is what I, as a reader, long for and enjoy most.
As a writer, both good writing and good storytelling is my main goal.