If she's not even a great enough author to engage you, she's not a great author. Regardless of the subject matter, regardless of whether or not you're "interested in children's fantasy" - a great author should engage you in their material regardless.

I wouldn't be boycotting your opinion in particular except that you are not content to say "I don't even expect you to agree with me that she's great". Instead, you want me (but don't expect me) to accept that she's great. It's insulting language, especially from somebody who, yes, has not read the books. No, you're not allowed an opinion on her works until you finish reading them (or at least one of them), just as you're not allowed an opinion on Monet unless you've seen more than 5 square inches of Water Lillies.