What I like about historical novels is the feeling of god-like superiority that comes from knowing things that the characters don't yet know. I've just come from reading Barry Unsworth's Sacred Hunger, set in the slave trade of the 18th century, and Ian Pears' An Instance Of The Fingerpost which is wrapped up in the scientific discoveries of the late 17th, to Hilary Mantel's chest-thumping Bring Up The Bodies, which is all about Thomas Cromwell and Ann Boleyn.
In the first two books you feel your knowledge of the way things turned out might give you an advantage over the key characters. Not so Thomas Cromwell. The character in Mantel's book has burrowed so far into the hearts of men that, even with the advantage of a further 500 years of history, you suspect you really couldn't tell him anything at all.