I find her portrayal of Tudor London to be convincing and vivid. Stories set in a different world - whether historical, fantasy or SF - must tread this balance of making the people in the other world people like us, but not people 'like us'. They aren't modern people thinking 'Urine in the streets? WTF?' but neither are they Merrie Olde English. Particularly in this historical drama which is driven by scepticism about current society and religion, but not the scepticism of people who know what comes next.
It's almost impossible to read some old style historical fiction because the cod 'period language' is so annoying 'God's blood sirrah, whence camest thou hence?' or some such gubbins. Mantel's language has virtually none of this, to the extent the language definitely isn't authentic - but I think she would say she was updating speech to nearest modern equivalence. Once or twice (I think perhaps once in what I have read so far) I winced because I thought she'd gone over too far into modern idiom.
So, I think it's a strongly-written historical novel, written from a good understanding of the period, about interesting people at a crucial time in the birth of modern Britain. I think it takes an unfashionable secular-humanist anti-aristocratic stance, which I like. Compared to The Little Stranger it is more realistic, more rooted in a story model where things definitely happen, and a plot unfolds. The cleverness is about clever ideas, rather than a meta-story. So, I probably would vote for Little Stranger, but I'm reading this with great enjoyment.