It's true that Shinigami exist in many other anime/manga, but I like how everything is set up in Bleach, and how Kubo-sensei carefully thought out everything from the concepts regarding the separation of body and soul (spirit exchangers, soul-sleep, etc) right up to the Gotei 13. And I haven't come across another anime with a plot like that of Bleach - maybe I just haven't watched enough Shinigami-centred anime. I don't know. And the characters' abilities - you gotta admit they're pretty impressive.
I'd say Bleach has plenty of originality.