Similar to others on these reviews; I think it only has a lower rating because of character relationships more than the plot line.
Yes there are plot holes, yes it's a little slow in places but overall it's great, especially if you're happy to just sit and watch it without over thinking. Such a breath of fresh air and love the concept. The sets, dress and wardrobe is great too which really helped contrast the different time periods.
By the end of the series you really come to love the characters and the ending is great.