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