I've just finished that one too. Started it after watching the series. I hadn't heard of her before but thought it was really readable. It was interesting to impose the character portrayed in the Mantel series (or am I just thinking he was actually Mark Rylance?) on the one in her book. I liked the Cromwell in the series but I'm not sure I would have liked the one that Borman outlined.
Yes, I thought it very readable, too, though - perhaps - I would have liked to see a bit more made of some of the sources that she did use.
The TV series (Wolf Hall), Hilary Mantel's books, the RSC stage adaptations of the books (which I saw in the Aldwych last August - superb) and indeed, Tracy Borman's book all sketch a number of character arcs, or which Thomas Cromwell's own is only one.
Henry VIII himself is another, and his transformation from a winsome talented Renaissance Prince, to the capricious, cruel and bloated creature he had become by the end of his reign is another fascinating arc.
The thing about Cromwell though, is that historically, he has been painted all white (much of the stuff written in earlier centuries, and the writings of the mid twentieth century historian Geoffrey Elton, to some extent), or all deepest black, when any reading of the sources or the era should see the various shadings of grey.
And, at the end of the day, whatever about the horror of some of what he did, virtually all of it was done in Henry's service, with the aim of carrying out the King's - either stated or implied - anticipated or actual wishes.