The Wheel Of Time Series
by Robert Jordan
At 13 volumes and counting, this sweeping — some would say sprawling – richly imagined epic chronicles the struggle between servants of the Dark One and those of the champion of light known as the Dragon Reborn.
Would probably be in the top 5 if Jordan would have kept the series at his originally planned 5 books. The first 4 books were some of the best fantasy I've read since Lord of the Rings. Unfortunately, under pressure from his publisher to keep a successful series going, Jordan kept agreeing to extend the storyline, first to 7, then to 10, then to 12 books, he actually died before book 11 and another author has taken over, which I believe the new author has agreed to ANOTHER 3 books. (I gave up after #10.) Unfortunately, Jordan's original story line never changed from his original plan, so most of the content from book 6-10 are essentially "fluff" and the core story moves at a snails pace. To put it into context, Imagine if J.K. Rowlings would have agreed to extend the Harry Potter series from 7 to 14 books. However, the story didn't really change, she just "padded" the original 7 books with pages of detailed descriptions of Hogwarts, dozens of characters that are only vaguely related to the story and many pointless story arcs not remotely related to the main plot.
Yea, most after 6 were fluff, but Brandon Sanderson has picked up the pace in the last 2 - including the much-awaited return of a character that was missed - and is working on the last one. the final book will be most bittersweet, since I’ve been reading the series since college.