Sword of Shannara is, I think even by Terry Brooks' admission, super heavily influenced by Lord of the Rings, he just added in the post apocalyptic stuff. I mean almost everything in Sword of Shannara has a pretty direct analog to Lord of the Rings. The Sword is the One Ring and Orl Fane is Gollum. The fellowship of the sword has Allanon for Gandalf, Shea and Flick for the Hobbits, Balinor and Menion for Aragorn and Boromir, Durin and Dayel as Legolas, Hendel as Gimli. Stenmin and Palance are Grima and Theoden, Shirl is sort of Eowenish, but really she's just a strong woman in a traditionally man dominated fantasy setting. And obviously the Warlock Lord is Sauron, but the ancient evil that can only beaten by a long lost mcguffin isn't exactly a fantasy trope original to LotR.
Elfstones and onward seem to be completely original creations though. Shannara really is one of the most engaging fantasy worlds out there considering you don't really see a setting where someone explores before the apocalypse, during the apocalypse, and so far after the apocalypse that it's practically a new world. It's a shame that he put me off so hard when he decided to have someone raped to death by Mwellrets, because I haven't touched one of his books since I finished Morgawr.