Of all of the various genres of fiction, I like well-written Alternate History the best. The trick, of course, is the 'well-written' part - and AH is harder to do right than other areas. For one thing, you have to be right-on in your typical writerly tricks - good storytelling, literate, good plotting and characterizations. You also have to be ACCURATE in a dozen different ways as to the projection you're making. - and that part is hard. It means you have to be something of a economist, sociologist, a good historian, get your military references right, and lots more. You can't be as sloppy (in my mind) as some who write fantasy; it is a genre that demands accuracy, and as little suspension of disbelief as you can manage. People have to say - yeah, that makes sense - that's how it would have happened in that case.