Witchcraft
I assume the witchcraft was true to the source material (the book), but every time I saw Elizabeth, her mother and/or her daughter (Elizabeth) casting a spell, it really detracted from the show for me.
I don't mind other characters accusing Elizabeth of being a witch (that is true to the time), but to watch her actually cast spells was ridiculous.
I wouldn't even mind them showing her cursing her enemies and leaving the outcome nebulous, but in one scene she cursed Richard's sword arm, and in the next scene Richard says "Ouch, my arm hurts." I mean come on!
Otherwise i thought the series was well acted and very true to history.