I've never read them myself, but I have read up on them. From what I've heard, the TV show is quite different from the books, so much so that in some areas, the TV show is better eg. Anthony is a much bigger AH in the books and is borderline abusive to Kate, Benedict in the books is more like Colin in the TV show and Colin in the books is more like Benedict in the TV show, Eloise isn't the outspoken feminist she is in the TV show and she's the one who witnessed their father's death rather than Anthony, etc. If you want to check it out, cool!

I've heard they aren't.

Pre-existing fans of the book would say otherwise, of course, but people who have tried reading the books because they like the show generally don't like it.