Set in the far future, after civilization has been destroyed in a series of wars, leaving the planet in a medieval state in which magic has become possible and there are elves, trolls, dwarves and such, the Shannara books are fantasy with a touch of sci-fi. Brooks has written around two dozen novels set in the universe, 20 of which have ended up bestseller lists, so this material is not short on fans. The TV adaptation would begin being based on the second novel in the original trilogy, "The Elfstones of Shannara" (first published in 1982).
A film adaptation of "Shannara," planned to start with the same book, was in the works at Warner Bros. for years, with Mike Newell at one point attached to direct. The company's hold on the rights ultimately expired, freeing up Brooks to pursue this TV version, which will be shopped around to networks once a showrunner and director are locked in. You can expect more swords and sorcery on a small screen near you soon.