One of my goals as an author is to not to always write the same kind of novel. I don't want to be stuck in one particular genre. Sure, I will probably have some recurring themes, but one story may be speculative while another may be a western, and the next a mystery thriller.
My first rule of writing is to create something that I would want to read; I write for myself, in other words. With that, I've enjoyed reading a variety of genres - science fiction (Asimov, Clarke); mystery (John Straley); action-adventure (Clancy), and literary (John Irving, Umberto Eco) to name a few.
Also, I don't want my work to be predictable. One of my favorite authors is Iain Banks because when I crack open one of his books I've no idea what I'm getting myself into. All too often I've enjoyed a particular writer (or filmmaker, or band) only to not want to read them ever again because they simply become a predictable derivative of themselves.
When it came to market my book, I had to put it into some kind of category, wherein I discovered the wonderfully ambiguous and interchangeable labels of literary, mainstream, and contemporary - the perfect homes for writing that doesn't adhere to strict guidelines of any one genre.
The irony here being, of course, that literary, mainstream, and contemporary are considered specific genres.