Hmmm, are we talking "series" as in "including trilogies and quartets" here, or does it have to be more than that number?  Also, what about works that were intended as one (very long) book but are traditionally broken up into several parts that are published separately (like Tolkien's Lord of the Rings) and books originally published in several self-contained parts but now frequently combined into one omnibus volume (like Stephen King's Green Mile)?

Anyway, starting with the beasts that nobody can legitimately dispute are series and moving on from there, based on the assumption that it's "yes" to all of the above:

MULTI-BOOK SERIES ( >5 INDIVIDUAL ENTRIES)
Terry Pratchett: Discworld
J.K. Rowling: Harry Potter
C.S. Lewis: The Chronicles of Narnia
Sheri S. Tepper: The True Game (all nine books, including the Mavin Manyshaped trilogy and the Jinian / End of the Game trilogy)

TRILOGIES / QUARTETS / MULTI-PART OMNIBUS VOLUMES
J.R.R. Tolkien: The Hobbit and The Lord of the Rings
T.H. White: The Once and Future King
Tad Williams: Memory, Sorrow and Thorn
Mary Stewart: Merlin Trilogy
Stephen King: The Green Mile

JUMPED THE SHARK
Anne Rice: The Vampire Chronicles

Unsurprisingly, almost all of my favorite supernaturally-tinged series are fantasy -- and I read both Green Mile and the Vampire Chronicles for pretty much everything but their horror contents.  That said, Rice jumped the shark for me when she insisted on using Lestat (of all characters) as a vehicle for exploring her rapidly altering expressions of faith ... shortly before going BBA and thus earning herself a place on my no-go list once and for all.  I still like the first books in the series, though, especially the first two.

One of the classic SF/F always been meaning to read.

For booklikes book club at http://booklikes.com/book-clubs/50/virtual-speculation 

(original review, 1987)

“The Gate to Women's Country”, remains the best written and most provocative of the lot when it comes to Feminist SF. It's one of the few books where I turned the last page and flipped back to the first and read it straight through again when I realized how deceptive the text, itself, was. I love when Septimus Bird tips Tepper's hand by noting that all good magicians keep us riveted on the left hand when the real trick happens in the right. That ends up being an ingenious clue about the ways we, as readers, are about to be hoodwinked. It's the very rare book that surprises me (my wife swears I have a seventh sense for foreshadowing; and I thought I was just a regular guy...) but this one did;

If you're into stuff like this, you can read the full review.

If I had read this when it was first published, in the 80s, I think I would have really liked this book. Alas, I read it now and it mostly made me angry.

This book channels second wave feminism pretty heartily, and unfortunately it also falls into some of the movement's pitfalls. Powerfully negative attitudes towards men lie the foundation for this story - an idea that men are innately violent and aggressive, and women are not, is the true dividing line. This book pretends that personality is based purely on nature with nurture making little difference. Bodily autonomy and emotional connectivity fall to the wayside in favor of eugenics and manipulation. And to make it even worse the lack of gender non-conforming or non-heterosexual individuals in this world is not an oversight - the book flat out states that queer characters were bred out (see page 76 in my edition). To say that the story is misandrist, gender essentialist, and aggressively heteronormative would not be inaccurate nor unfair.

As much as I wanted to throw this book across my room at times, or to give it a half star rating, I will give it some credit where credit is due. This book is of its time, and it came from an angry place. And I get that. I've felt that. A lot of people have. It is interesting to use science fiction to play around with thought experiments, and our book club had an excellent discussion about this one. Tepper quite obviously put a lot of thought into her world, and the world-building was fairly intricate. The characters were drawn well enough that I truly hated many of them, and some mirrored individuals I've known in my past. There are some really excellent insights in here, and even passages that I reread because they struck a chord with me. However, I just couldn't get past the politics. It's a great book to talk about and critique, but it is not a book I feel I can recommend outside of that capacity.

Plaque, teleportation, mind control and wiping, monster killer "horses" called Hippae, monster "foxes" called foxen, a planet covered almost entirely in grass, fox hunts, a long dead alien race called the Arbai.... these are a few on my favorite things.

This is a great story. While some of the characters seemed a little shallow at times, the story moved at a good pace. I must say I was a little surprised with the ending.

Highly recommended!