It's really only Pillars of Creation and Naked Empire that are truly bad and uninteresting on almost every level (the former mostly because Goodkind was delusional enough to think it would be a good idea to write a book in which the main characters of the series, and the main plot of the series, get all of fifty pages of screentime). But to say the dislike of him is only because of his attitude and his preachiness, well, not entirely, though of course those two things are the main issues. But take both of those out, and you still have a series that, while entertaining, doesn't have much depth. Other than that, Richard's perfection and Mary Sue-ness is rather grating, some plot twists are contrived even by fantasy standards (though they mostly happen due to Richard's perfection and/or the Objectivist ideology, I suppose, so maybe I shouldn't list that separately), and the excessive violence is distasteful, particularly when perpetrated by the good guys and hence supposedly something to be approved of. Oh, and he has an annoying habit of recapitulating the plot of earlier books in detail, though I'll admit at times that's useful for people who don't bother rereading before a new book comes out. Those are the main points against him, I think.

As for points in his favour, his other characters aren't bad and sometimes even quite good, and he can write compellingly when he isn't preaching, with occasional moments of brilliance (the first sentence of Faith of the Fallen comes to mind). In the case of Faith of the Fallen, he even wrote compellingly while setting out his ideology, but after that he mostly limited himself to the lame preaching.