Contrary to revisionist opinion, this is a deeply emotional and meaningful series that touched on, among other things, alienation, humanity, parenthood, forgiveness, and altogether humane behavior. A transcendental series if watched with the right mindset. The blood and gore only adds to the atmosphere, they are nothing in themselves.
If you are childish or have childish reflexes on things such as revenge or hate, this may do you a lot of good.
Elfen Lied is glorious beyond mortal knowledge.