This is a personal list of epic fantasy book series I know of. Epic means at least 3 books in a series (aka Trilogy or more) and no less than 1.000 pages in total. The list is sorted by the Goodreads Rating (2017) which may change over time.
The Stormlight Archives
Brandon Sanderson
Goodreads Rating: 4,57 #Books: 3 # Pages: 3.894 Year Started: 2010 Year Finished: not yet
The Kingkiller Cronicle
Patrick Rothfuss
Goodreads Rating: 4,57 #Books: 3 # Pages: 2.178 Year Started: 2007 Year Finished: not yet
Harry Potter
J.K. Rowling
Goodreads Rating: 4,47 #Books: 7 # Pages: 4.101 Year Started: 1997 Year Finished: 2007