Usually, when people laud an artist's orginality, I think the implication is that they appreciate the fact the artist is providing them with a sound they haven't experienced before. That may seem tautologous, so I shall try to clarify what I mean: If one artist rips off another artist, as long as the listener isn't familiar with the earlier artist's work, a lot of the time they will be able to appreciate the newer artist as if they are truly original. The artist's sound will still be new to them and that is what matters; whether it is actually original or not does not.
To me, however, originality has its own inherent value, to the point that, if I hear a song, like it, then later find out it is a rip-off of another song, I will frequently be unable to enjoy that song - or even the artist responsible - again. That will be it. The song will be ruined for me. Which I'm aware is an incredibly contrived approach to listening to music, but that's how it is.
I've felt this for a while, but I began giving it specific thought again recently when I heard The Tallest Man on Earth for the first time. The song was pleasant enough, but I could not get past the guy's ridiculous debt to Bob Dylan. Of course, Bob Dylan is hardly the worst person to attempt to imitate, and it's not like I have such a huge Bob Dylan collection or have spent so much of my life listening to him that I no longer have any time for somebody who sounds similar It was simply the fact The Tallest Man on Earth sounded like another artist that put me off.
Anyway, those are my fairly unstructured ramblings on the matter; please feel free to share your thoughts.