Firstly as reader of the books which I loved, I find the TV series a bit different but has to be expected when translated to the screen. I really like the casting which I think is excellent particuarly Matthew Goode as Matthew Clairmont and Teresa Palmer as Diane Bishop, albeit Teresa's accent sometimes swaps/merges with her American/Australian accents, the latter which can be quite flat.
The richness of the scenery on location and on set, are fabulous especially Oxford and the sets at Matthew's house and Sept Tours are magical. A lot of this must be enhanced by the excellent photography/filming which is so rich in colour, this provides exactly the perfect ambience for the story.
Bearing in mind my own love of fantasy based stories, the combination of all the above make this TV series one of the best I have seen, and I would 100% recommend it, for all of the above reasons.