Was impressed with the final episode (watched the whole thing as oner on iPlayer), especially the siege but a little bit disappointed with the series as a whole. I never quite got why they had to introduce things like the peine forte et dure (which was used against those who refused to plead but not on any contemporaries in 1605) when there was plenty of brutality and nastiness against recusants and any priests discovered in England. Fr. John Gerard certainly led a dramatic and charmed life but I did raise an eyebrow at Catesby helping him to escape the Tower!
That said, the casting was very good. Kit Harington was very good as Catesby as were Fawkes, Garnet James I/VI. I also liked Mark Gatiss as Cecil - definitely a much more nuanced villain than Waad/Wade!