I think Cromwell's been given a very hard time by writers. In fiction and drama he's been caricatured as an evil figure in a black cloak, lurking in the wings with dishonourable intentions. In biography his essential self is missing, because his private life is almost entirely off record.
David Starkey's phrase works wonderfully (Note - David Starkey referred to Cromwell as 'Alistair Campbell with an axe') to alert you to Cromwell's role as a propagandist for Henry, but Cromwell was a lot more subtle than Alistair Campbell - or at least more subtle than the popular picture of Alistair Campbell suggests. Cromwell didn't deploy his heavy artillary unless he needed to. He was a persuader, negotiator and, to a degree, a compromiser.
I think the picture darkened with the Victorians. Cromwell's image hasn't always been bad: in Elizabethan legend and literature he was a hero, but to the Victorians he presented a problem. He wasn't a varsity man. Historians couldn't get their heads around the idea of a member of the lower orders rising so high in the hierarchy. There was a sentimentality about the medieval world, with Cromwell seem as one of its destroyers. The idea persists today.