The best stories for me, create a newness out of activities I've seen or read about before. We've all read a story about two people that fall in love... the best stories take that basic concept and turn into something that's surprising, fresh, and unexpected.
Style is also a big thing for me. I read to be inspired, so when I'm exposed to different styles and voices, it really does excite me. With that, of course, comes plot, character development, etc. But how one author chooses to do those things compared to another is really thrilling.
With that said, I have the tendency of making up my mind about a story very shortly in. I'm ADD and a sucker for a strong hook or else I'm afraid I won't continue reading. It's a habit I'm trying to break because some of the slower starting works I have read ended up being brilliantly well written and well paced pieces by the end.
Just my thoughts,
J.