It was a very good series and we would have given it a five star rating except for the really annoying modern music that did not fit the period being depicted. It was irritating, to put it mildly.
Not being Irish, the non-authentic accents did not bother us but I can see why people from the Republic would be.
Finally, we found the acting and character development to be very good. The series motivated us to read up about the Guinness history on Wikipedia from its founding in 1759 on. My wife actually visited the Brewery in Dublin even though we are not beer drinkers.