Not a big reader of the Giant Novels anymore, or reader of big series, but I can name a few.
My favorite, and the only one I'm currently reading is not really a Novel series, the books (Except for the last one which is extremely long) are not excessively big, but it is a LARGE series.
Lone Wolf (31 Books in the Main line currently, 4 World of Lone Wolf Books, 12 Legends of Lone Wolf Books, two Side Novels by other authors, a (I think) 3 books series called Autumn Snow (by a different author), the Skull of Agarash Comic, and the Magnamund Companion.
Other Book series that I've dabbled in or read in the past that may be considered to be Long with big Novels...
The Shannara Series - This has like 29 Books and several Novellas (collected in yet another Book). The biggest and longest ones are probably the First 3 though. I really enjoyed it at the start. Once he starts going more fantasy punk sci - fi it grew less interesting. When he started involving adult subjects...it REALLY lost my interest.
The Sword of Truth Series - 21 Books, many of which are pretty long. I never really got absolutely into this one, but it's one of those with Long Novels in a Long series.
Thomas Covenant - This is not as big a series of books as others, though the Novels can be lengthy. Only 10 books in this one. Has some uncomfortable adult themes.
not long novels, another book series similar to the Lone Wolf Game Books...
Fighting Fantasy had something like 59 Books when it ended years ago, and then it got resurrected. I have bought something like 5 or 6 more of them which were added on in this century (so at least 64 or 65 of them total).
Promising...
Brandon Sanderson's Books tend to be long. The Stormlight Archives tend to be extremely long in length. He's finished Book 5 of what he says is a 10 book series, but who knows if he'll add on to it after that.