Wolf Hall is every bit as good. It may not be up there with War and Peace or Gravity's Rainbow, if we count those as historical novels, but it need not blush to stand alongside the historical novels of F. M. Ford, Graves, Yourcenar and Vidal.
One great quality of Wolf Hall is that it assumes you already know what an educated person ought to know about Tudor England. Most historical novels assume you know next to nothing about the period when the fiction is set (most readers of historical fiction, unfortunately, justify the assumption), leading to great lumps of exposition, often in the form of one character giving a lecture to another character, catching the reader up on personages and events at the expense of narrative pace and verisimilitude. For reader for whom historical fiction is a substitute for reading history, all this exposition is crucial, even desirable. And thus we have the corpus of James Michener.
Mantel is different. On p. 19, the novel's chief character, Thomas Cromwell, learns from his employer, Cardinal Wolsey, that King Henry VIII has decided his wife the queen will never be able to bear him a son, and so insists on a divorce and a new wife. No mention yet of Anne Boleyn, Martin Luther, Thomas More, etc. -- just a conversation between an ecclesiastical powerbroker and his trusted right hand about how tricky this business could be. Most historical novelists would be in exposition overdrive at this point, or frantically signalling how shudderingly important all this is -- Tudor history, and a lot of European history, teeter on the outcome. But Mantel doesn't bat an eye. No tiresome lectures, no ominous chords on the organ... just two men talking about a troublesome matter that has come up at work. After all, neither Wolsey nor Cromwell knows, Henry does not know, no one knows all that will shake out here...so the narration does not know either. Mantel knows, you the reader (should) know, but leaving the unfolding-drama stuff tacit makes the scene dramatic.
Okay -- second point. Cromwell. Brilliantly imagined. Famously intelligent, brutal, cunning, the English Machiavelli and so on, the blustering heavy of Robert Bolt's Man for All Seasons. Mantel's Cromwell is intelligent, cunning, capable of brutality even, but he is compelling and captivating, too, from the very first paragraph when he rises from the dead -- well, strictly speaking, he comes back to consciousness after a savage beating from his father, but it's as if he is able to learn from every punishment fate hands him and come back stronger, turn adversity into opportunity. What does not kill him makes him stronger -- and for the length of this novel, nothing is strong enough to kill him.
He is a self-fashioner in the Greenblatt sense, his personhood a work of art and learning, not something he was simply born with -- he runs rings around the boobies who think their birth entitles them to place and power. He survives not only his abusive father, but the perils of war and trade, and the perils of loyal service when Wolsey falls -- by staying true to his man as Wolsey suffers disgrace and death, Cromwell ends up Henry's most trusted man, the most powerful non-royal personage in the kingdom.
There was to be, eventually, a fall from which Cromwell could not rise, and it is faintly foreshadowed when Cromwell turns in the last paragraph towards Wolf Hall, home of the Seymours -- again, you have to know some history to catch the tone here -- but we bid him goodbye at a crucial moment, when he has caught More on the hip and sent him to where saints go. Mantel's More is also compelling imagined -- intelligent and of adamantine integrity, as advertised, but arrogant, proud, cold, maddeningly legalistic, fully capable of sending heretics to the stake when he had the power to do so.
Final point -- Mantel is a magnificent stylist. Take this passage of Cromwell ruminating on the old superstitious England that he, as Self-Made Modern European Man, believes ought to wither, but which is as unwilling either to change or to disappear as More, and like him is ferociously clinging to its existence. More is refusing to swear to an oath that Anne is queen and her children the legitimate royal heirs, and Cromwell imagines the rest of Olde England likewise refusing to swear:
Who will swear the hobs and bogarts who live in the hedges and hollow trees, and the wild men who hide in the woods? Who will swear the saints in their niches, and the spirits that cluster at holy wells rustling like fallen leaves, and the miscarried infants dug into unconsecrated ground: all those unseen dead who hover in winter around forges and village hearths, trying to warm their bare bones? For they too are his countrymen: the generations of uncounted dead, breathing through the living, stealing their light from them, the bloodless ghosts of lord and knave, nun and whore, the ghosts of priest and friar who feed on living England, and suck the substance from the future. (471)