That the writer can keep you entertained and enthralled in reading their book. A good writer will just get you involved in the story so you won't want to put the book down. Good knowledge of the subject that is written and a good story teller. I read a lot so I know a lot of great authors and I also know some that are just OK. It's how they can keep you interested in the story that counts.
A good writer writes from the heart......
You have to keep the reader engaged in the story. I'm writing a story myself and I'll keep re reading it as a reader and imagine what I think would happen. It''s a great thinking tool that makes your story all the more exciting (technically I'm writing my story still now and I'm midway through it ) hope I helped
That whatever you write, its what you're writing that makes you creative and your story very unique and impressive. That's all I got.