Season 1 is the closest storyline to the books. Season 2 and 3 cover the high points but change parts of the storyline. Ysabeau is younger in the books, the Knights of Lazarus' role was greater and members different, and Matthew was much more protective of Diana in the book later in their relationship (to name a few).

I enjoyed the Season 1 thoroughly. Season 2 the pace and story line felt off and Season 3 was shorter so it skipped much of the book hitting the main points and changing some of the story and which characters arcs.

Overall, if you have not read the books, the three seasons are well down. If you have read the books, which are very good, you will likely recognize the missing or modified storylines.