This suffered from what so many dramas starring teens have a problem with - the main actors, including Isaac Calmroth playing Erik, are several years older than their purported ages, much older in fact. It doesn't do much for verisimilitude.
Nonetheless, I enjoyed the series and would have given it an eight had the story not been changed to match some notion of political correctness. For goodness sakes! The action took place sixty odd years ago. Applying modern notions to a brutal story of the dreadfulness of Sweden's past just didn't cut it. Some of the scenes were true to life such as the scullery maids curtseying to the Matron, but notions of noble holding back in the face of overwhelming violence and wickedness are alien to the timeframe. The original book was far truer to the times than the series.
What came across really well in the series was the dichotomous nature of Sweden, proclaiming openness, social democracy, freedom, liberalism while in fact, horrors were going on both hidden and overtly.
Despite my reservations, I recommend this and watched it all over a two-day period.