I absolutely loved this anime
When I was watching the first episode, where it starts with Lucy breaking out, all splatter and stuff, I was really close to just dropping the anime immediately because I'm not that much into splatter.
But I kept going and it definitely was the right choice.
I enjoyed the anime so much that I watched through all the episodes in merely 2 days (whilst going to school as usual).
I think it's absolutely fascinating, it's very deep (relationships between characters, characters past etc - even a little philosophical), full of emotions (don't think I cried that much watching some sort of movie ever before...) and it's got a really good and solid story.
I definitely recommend Elfen Lied to everyone who isn't only looking for entertainment and fun in an anime but also for something "deeper".
This anime won't leave you happy but it'll leave you deeply impressed and thinking.