I’m using the term “epic” a bit loosely here, but my main intent is to break away from classifying it as an “epic” novel on the sole basis of its length. For example, Lord of the Rings is obviously an “epic” series of books, but it manages to tell its story while keeping each book’s length to that of a pretty standard novel. That doesn’t align with more modern fantasy series where each entry in the series is around a thousand pages long.
You could contrast that with, say, Malazan Book of the Fallen. It’s hard for me to tell someone “oh yeah, you should totally go and read this 10,000 page story”, you know? Assuming a standard novel is 400 pages in length, recommending that someone read Malazan is the equivalent of reading 25 books, which was the totality of my Goodreads reading goal for this entire year! So, clearly, it doesn’t make much sense to recommend such a thing to someone, to just offhandedly suggest that they spend the next year of their reading time on what is essentially just one story, setting aside the vast multitude of things the average reader typically likes to read, like nonfiction, biographies, mystery novels, spy thrillers, etc.
That said, “epic” books are obviously a lot of fun. So what are some books that are not of gargantuan size, or perhaps series that are very digestible (ultimately I’d say Harry Potter is probably more on the “digestible” end, but the overall length is perhaps pushing it), but would still be classified as an “epic” story?
As an example, I’d absolutely consider Dan Simmons’ “Hyperion” to be epic, considering that it’s about a galactic war and tells a story from such diverse points of view that it feels like multiple novels crammed into one, and it pulls this off in less than 500 pages. (granted, there’s a follow-up book to resolve the storyline, but that still functions as its own book and is, once again, standard length).
for a non SF/F example, E.L. Doctorow’s Ragtime is a sweeping novel that chronicles the first decade of the 20th century through the lives of three families in New York (one WASP, one Jewish, one Black) and dozens of historical figures. It comes in at under 300 pages.