I am currently reading an extremely-long (14 volumes, each about 1000 pages) fantasy novel serial called the Wheel of Time, by Robert Jordan (the pen name of James Oliver Rigney Jr. - 1948-2007) the totality of which was published between 1990 and 2013, having been posthumously completed by Brandon Sanderson.
I say 'reading' but in fact I am listening on audiobook - the readers are the husband and wife team of Michael Kramer and Kate Reading - who are first-rate exemplars of this difficult craft.
I came to Wheel of Time via the wonderful novels of Brandon Sanderson, who completed the series; and a further link is that Sanderson's audiobooks are also done by Kramer and Reading.
Apparently Jordan's The Wheel of Time is very well known in the USA, where it was a 'best seller' - that is not the case in the UK; where these books are not stocked by shops or libraries.
It is a large commitment to begin such a long haul, and I rather doubt whether I would have done it if I had had to read rather than listen; but I am delighted by the experience so far. First thing every morning, and doing doing chores, and at other times - I listen to the books and am transported into a vast world populated by numerous characters.
What I like best about the Wheel of Time is that the invisible authorial presence, behind and permeating the text, is one of a wise and good man. That makes a big difference for me; because I find most authors to be ultimately untrustworthy - most good writers are, indeed, bad Men. 'Robert Jordan' was clearly a fine person.
The structure of the narrative is more like a serial than a single multi-volume novel or sequence of linked novels; when there is such extreme length, the overall story is backgrounded, and functions mostly as a thread to join-up the various scenes, and from which to develop character. The books are capable of depicting beauty and horror, moving me to tears, making me laugh, and sustaining my attention and interest. As a prose stylist Jordan is therefore good-enough - but not great or special.
(Something similar applies to JK Rowling, and to several other major fiction writers such as Charles Dickens. Not all great novelists are great writers - and most great writers are not great novelists.)
Why is the book so very long? The main reason is that there is a large cast of characters - six main characters, but dozens of others from whose perspective we get to see things. The reason why the books are long is the detail - the scenes are described in more minute detail than I have come across elsewhere (except, significantly, in Brandon Sanderson - who I guess may have learned this from Jordan). Reading the scene therefore takes longer than the scene would take in real time - which is a 'Wagnerian' way of doing things.
(Wagner's operas, or at least the late ones, can be enjoyed only once it is understood that events on stage are happening in 'super-slow-mo'; the orchestra, not the voice, describing the smallest nuances of what the characters are thinking and feeling.)
The main strength of Wheel of Time is that it does extremely-well what Fantasy is supposed to do: it makes an inhabitable world in which the eternal and essential human things are dominant - a world of truth.
The importance of Fantasy is that the everyday modern world is one of lies and triviality; so people like myself almost need the Fantasy genre in order to 'exercise' the proper priorities and evaluations.
If you like the sound of what I have indicated, then I would recommend Jordan's Wheel of Time. Don't think of it as being 'like' some other author. WoT does what it does supremely well - and it is a delight to be able to enjoy it day after day, week after week, month after month... and still not have reached the halfway mark!