As a fan of the Herriot books, I was excited to see that they had made a TV show based on the stories that Herriot carefully wrote about. In general, I think they did a great job of capturing the peaceful, loving, moods of the Herriot books and translating them onto the TV show. The hard work of the country farmers, the worry over the sick animals, and the humorous subplots of the quirky yet lovable characters of Tristan and Siegfried Farnon were well done.
I would give this 5 stars if they did not add the unnecessary plot of Helen being engaged. The last two episodes were overdramatic, and the changing of the plot was really unnecessary. It caused the show to move from being a show about a young and inexperienced veterinary surgeon to a romance story. Some may have enjoyed this, and I realize that the writers may have thought that viewers would prefer a little extra "spice".
However, I did like some of the other changes they made to the show. Ms. Hall was often a "background" character in books, and never really appeared much in the books. However, her role as a caring housekeeper, while also grieved mother adds an interesting dynamic, and one that I enjoyed.
TL;DR: A great show, and a pretty good adaptation of the Herriot books! Would recommend!