They are historical novels - (indeed, a bit like a sort of biography written as a novel). Mantel's prose style is exquisite, her learning profound (but lightly-worn and effortlessly woven into the tale), her characterisation superb, dialogue sharp and, historically, the books are very solid, although she doesn't mask her strong preferences (i.e. Thomas Cromwell, one of the traditional villains of this universe, a chap who represents the forces and values of a meritocracy (rather than inherited privilege), an almost secular moderniser with a sharp sense of humour, is her hero, while Thomas More, to give one example, the more traditional hero in tales of this era, is, by contrast, portrayed as an insufferable moralising intellectual snob with an appetite for martyrdom).
Actually, I can't recommend them highly enough. Mantel won the Booker Prize for the first of these books "Wolf Hall", which was published in 2009 and which ends with the execution of Sir Thomas More in 1535. The second, which has just been published, is called "Bring Up The Bodies" (a legal term from the 16th century referring to the command to 'bring up the bodies' from whatever prison cell they were held in, in order to physically stand trial), deals with the events of 1535-1536, ending with the downfall and execution of Anne Boleyn.
Initially, (according to interviews I've read) Hilary Mantel had planned to write about Cromwell, - a single book - but found that the material demanded much more detailed treatment. Then she thought it could be told in two books, but felt that the death of Anne Boleyn marked a natural ending to a second book. A third book is planned, which should bring the tale to its conclusion, with the downfall of Cromwell himself, in the summer of 1540.