Should you pigeon-hole yourself? Novelist and playwright Michael Frayn says yes, if you want to be successful. This is an excerpt of an interview with him in The Paris Review:
"Let me say for a start that I don’t think it is a very good idea to write different sorts of things. If I were to give serious practical advice to a young writer about how to succeed I would say, Write the same book, or the same play, over and over again, just very slightly different, so that people get used to it. It takes some time, but if you do it often enough, finally people will get the hang of it, and get familiar with it, and they’ll like it. Then you go on producing a consistent product and you’ll have a market for it. Because the consumer of books or plays, including myself, very reasonably wants to know or have some idea in advance what the book or the play is going to be like. It is the same as buying breakfast cereal: if you buy a packet of cornflakes, you want to be sure it will contain cornflakes and not muesli. It is very irritating if the packet doesn’t contain what you expected it to contain. Similarly it is a reasonable demand from the theatergoer or novel reader that he should get a constant product, which is identified by the author’s brand name.
If I could have done this, I would have. But I don’t have much control over what I produce. All I can do is to write the stories that come to me. And what a story is, is in part the way of telling it. A story is not an event in the outside world—it consists in the telling. It is only when you think that you have found a way of telling the story that you can start writing it. Different stories naturally suggest different ways of telling them. If I had been better organized as a writer, I would have gone beyond the stories’ dictates and imposed my own central imprint on everything."
Actually, even though it goes against our creative instincts, I agree with his advice from a career standpoint. Once you've established yourself in one genre, you can fight to expand your reach--and it will be a fight, but it's possible. Some authors handle this by using different pen names. Graham Greene did it by labeling some of his novels "entertainments" to distinguish them from the books he considered more serious.