While Elfen Lied tends to rely upon scenes of intense gore and utter depravity, it is surprisingly not without a storyline. The writers let the viewer hit the ground running in perhaps one of the most unsettling openings of anything ever, with several brutal murders. The fact that a certain female main character is naked at the moment will hardly register in anyone's mind. As the series progresses, you get long intervals of calm and thoughtfulness, but they never last long without someone getting ripped to pieces. And what's more, the situations the characters are put through make one feel genuinely sorry for them. If I have any complaints, they are that 1.) the anime is ecchi and thus has to make sacrifices, and 2.) the ending is perhaps too open-ended; I assume this is where the manga takes off from.
The animation in Elfen Lied was actually impressive. The animators didn't miss a beat in creating the overly vivid scenes of action, violence, and gore. In the calm moments, the animation is less of a focus, but that's certainly forgivable in light of the content. And of course, the characters each have a fairly individual look amongst themselves, which is rarely an issue for an anime of this caliber.
Each episode begins with the characteristic melancholy notes of the Elfen Lied theme. The theme alone is rather impressive and not at all a generic anime opening. Plus, variations on that theme appear all throughout the show as incredibly versatile background music. The anime also thankfully avoids excessive use of sound effects, already giving it an advantage over other ecchi titles. The voice acting was likewise superb.
The characters of Elfen Lied are less impressive than the rest of the anime. Some of the more minor characters were the most compelling, but the leads were either generic or simply bland. The male lead is all too typical of ecchi/harem leads, though his brief flares of personality do prevent him from being a self-insertion character. Surprisingly enough, the most compelling character was probably Nana, whose story of tragedy never seems to truly end.
In the end, Elfen Lied receives an 8/10 overall score. While I was positively enthralled by the anime as a whole, it lost something in the weaker characters and the ecchi moments. That said, I still consider this a great anime. It catches the viewer completely off-guard with its incredible violence and sinister implications, which just isn't seen to this extent in any other anime. If you want deeply disturbing, you've found it.
Watch this if: you want an anime that will shock and disturb you
Don't watch this if: you're concerned about how you will look having watched an ecchi anime