Science fiction is often unfairly compared with fantasy books for educational uses. This is a weak analogy because the two genres are so very different. The two are only related in that they both fall under a larger genre known as speculative fiction and are found in the same section in bookstores.
“It is also a story of superstition and fear and how it is overcome—by children.” —Rocky Mountain News interview with L. Ron Hubbard
Epic in its current use seems to mean a sort of meld of awesome (i.e., neat-o) and outstanding. Epic: “telling a story about a hero or about exciting events or adventures very great” or “large and usually difficult or impressive” This is the meaning that was in my mind after reading Battlefield Earth.