I just read The Host. And it is way, way better than Twilight. The writing in Twilight ... ah, the kindest thing I could say about it is that it really needed a good editor.
I don't blame Stephenie herself as much as I blame her publisher and, by extension, her editor. They saw the potential in her writing, they pushed the book out the door, and they didn't take the time to help her polish it and make it good. Her publisher is making bank. But she's stuck with a book that is not as well-written as the concept deserves.
The Host, on the other hand, has obvious signs that it's been well-edited. It's better structured. The romantic tension is better. Someone has taken a red pen to many (not as many as needed. But still many.) of the adverbs. There's better-developed conflict and growth.
So, yeah, I guess the author is ultimately the one responsible for the book. But. As an editor (I edit essays, not novels, but some principles are the same), I think she got a bad rap. She needs someone who will help her writing shine, not someone who tries to push the books out the door so quickly that they don't receive the attention they need.
And I think it was stinky of Stephen King to attack her. When was the last time he spent weeks at a time on bestseller lists? Professional jealousy, hmm?