Really enjoyed the books (though there is a sneaking feeling, in the last couple I've read, that Cornwall is a bit bored now and just phoning it in) I couldn't even make it through the first episode of the TV series which was utterly awful. I recommend reading the books if you have the time.
I have read all the Last Kingdom books and found them all to be mostly an enjoyable read. I believe Bernard Cornwell always meant to conclude the series with the epic battle of Brunanburh, which he did with "War Lord" which came out last year, even though the Uhtred character is 80 years old by this time

Some of the later books did feel a bit formulaic filling in time to get to this finale. I felt his account of Brunanburh was written more for dramatic effect than historical reality which, as a historical novelist, would be his preferred option I suppose.
I have really enjoyed the TV series. Perhaps you should have stuck with it. On Season 4 now and all get very good reviews although be prepared for it depart significantly from the story in the books as the series goes on.