Here's a thoughtful discussion, sparked by historical fiction author Mary Tod and continued in a whole series of lively comments.
Top Ten Ingredients of Favourite Historical fiction - A Writer of History
I think she's got a good list of the most common features of popular historical fiction. But I don't take it as a recipe for my own work, and I don't suppose any serious writer would. For me, the aims of re-imagining events of the past are, first, to learn something that might be useful in our future actions, and second, to understand better how things got the way they are. My novel about the 1402 Ottoman siege of Constantinople (A Gift for the Sultan) is really about how any great city draws on its most diverse resources when under tremendous stress, and also about how such a polyglot, multiethnic and territorially expansive system as the Ottoman Empire (with all its consequences down to the Balkan wars of the 1990s and Syria today) got its start.