When I pick up a book, I'll admit that I'm more tempted by a good quality hardback cover with a clean design than I really should be. However, when making decisions, I make my choices based on good reviews, the author or by shutting my eyes, swinging my arm and seeing what I end up pointing at. My first and greatest dislike would be stories that strictly follow a genre. Is real life composed of genres? No - so why must stories? Fantasy, horror, drama, mystery, romance - nothing beats a story that mixes it all up into a big multi-genre soup. I also prefer stories that focus on the one protagonist throughout - it makes the story more personal and allows you to discover the events, mysteries and revelations exactly as the protagonist does.
Originality is a tricky issue. Whilst nothing beats a very unique story that is unlike anything ever written, the portrayal and depth of the story is far superior. For example, the Lord of the Rings is a very famous story that has been completely squeezed dry, but if it were to be rewritten using a less wordy style with extra attention taken to the characters, it would be worth reading again on its own.