Some locations and ideas from the Shannara series are fascinating, no doubt about that - Paranor is forbidding and quite creepy, for example, and it conjures the image of this dark, empty castle devoid of life except for that of the current Druid, a castle that was thought for an Order and was now inhabited by a single being.
However, I agree that the first book, Sword of Shannara, heavily copied LotR ( with Allanon in Gandalf's shoes, Shea and Flick in Frodo and Sam's, the prince whose name I don't remember in Aragorn's, and even the story structure was identical, with Allanon coming to Shea, revealing secrets, then going away promising to return, then sending someone in his stead because he couldn't return in time/meet Shea in time ).
Spoiler:
The idea of a sword that has the power to reveal truth and the idea that truth itself is the only weapon that can affect a being that lied to itself about its own life is original, though...
The Elf-Stones of Shannara was good enough, Wishsong less so ( although the characters were better developed ), but the Scions series was not very good and it already began repeating itself ( possibly the only part I enjoyed was:
Spoiler:
Walker Boh's journey to recover the Black Elfstone from the Stone King, Quickening's sacrifice, and the return of Paranor with Boh as the Druid.
First King of Shannara was better, but mostly because it showed many things and characters one could recognize from earlier books ( the black elfstone, for example ); but the trilogy of the Jerle Shannara was far below average in my opinion.
Spoiler:
Brooks's description of "technology" and his melding it into his world - even if it is our world after the Great Wars he speaks of - seems to me awkward - it lacks detail and intricacy and above all a way to make us believe in its possible reality.
I think the author's main fault is that he doesn't give much attention to detail and character development... for example, almost every author has made up "rules" as to how magic works, what you can accomplish with it, and how - it helps giving a feel of believability. Brooks's magic lacks this kind of details, and thus, it doesn't make me feel like what he's saying is believable, in my opinion.