One of the few shows that is fast-paced and makes you care about (like and also despise) its characters. The fourth season covers books 7 and 8 in Bernard Cornwell's Saxons saga but the plot unfortunately has become predictable.
This historical fiction is about Danes attack to Saxon land (modern day England), with many of the characters are rooted in history. The main protagonist, Uhtred of Bebbanburg who is the audience's main point of view is based on a fabled warrior who happens to be one of Bernard Cornwell's ancestors.
Uhtred is Saxon who was raised by the Danes. This makes him a misfit in both camps. Although he fights for the Saxons, they dislike him for not being Christian. Some of the Danes are more accepting of him, but they cannot forgive him for siding with the Saxons.
This premise was quite captivating, and I was (and still am, but to a lesser extent) a fan. Each season covers two books in Cornwell's series, and considering that he is going to end this saga with the 13th book, it seems the show has enough material for probably three more seasons. But much like every intellectual property that lives for too long, the creator(s) end up eventually repeating themselves. In every season, there are savage Danes that have a personal vendetta against Uhtred (the story's hero) and also scheming and conniving Saxons that try to stab Uhtred in the back. These characters are despicable and fun to hate, while Uhtred himself is easy to root for. With this pattern being repeated over and over, I worry that the remaining seasons (if the show gets renewed) will be a rehash of the same formula.
Season 4 of The Last Kingdom was still entertaining and enjoyable, and for this I'd give it a 7.5/10. But I do hope the show runners change a few things for the next season.