It's set around the 9th century, when Danish viking warlords land in what was then Northumbria, and England is ruled as separate Kingdoms (The concept of England was only just beginning to form). Its based around an Anglo-Saxon noble protagonist called Uhtred, who is adopted by a Danish viking family as a boy. After they are betrayed, we follow his quest both for vengeance and to reclaim the lands that belong to him.
It's got violence, druidic magic, PG-sex, gore, conflicts of loyalty, character building, emotion, religious tensions... All whilst being
mostly historically accurate It's wonderful
I can't do it justice at all though it really is amazing. You should give the first episode a try (although the later seasons are a lot better)