Its not deep, maybe emotional and touching, because the characters have strong emotional moments and generally make a good bawwwwwwww. It has "value", just not philosophical, because I've seen faggots claim it as a interpretation of the doomsday, or how mankind will kill itself, I've seen faggots talk about some mindless social problems and how the government is oppressive, but the only REAL deep I've seen in it is about intolerance towards the different, which is barely deep as its a common topic in most anime. This one just strengthens that trait.
So, in conclusion OP,
if you want to watch Elfen Lied, expect
1.Mindless Fanservice, as in blood, nudity and ecchi.
2.A emotional watch, since the show basically revolves around "happiness" and "sorrow" and "zomg revenge". Disregard the psy shit, I don't consider schizophrenia induced by tumor ZOMG SOOO PSAKOLOGIKLI DEEP.
3.A love triangle. Disregard the incest shit people talk about, in Japan cousins don't mind having sex and being in love with each other, its just another retarded view by people who don't know shit and yet go around spreading it. Also, nobody gives a fuck about that poor kid. She's a much better and useful character in the manga anyway.
Do not watch it for the DEEP meanings, its just a a bit above average anime. Not fucking ghost in the shell.