I won't bother explaining the plot, because if you're reading this you probably already know the gist of it. I will instead highlight a few of the plot elements that I thought were particularly inventive/touching.
It seems to me that Kouta is not so much a full-fledged character as he is a vessel for his sexual desire. Indeed, several major plot elements are influenced at least marginally by the influence of his libido. For example, Lucy's rage is quenched only because Kouta showed her forgiveness. Would his response be the same if Lucy wasn't a supermodel? Impossible to say, but I love how the plot is moved by the serendipitous, arbitrary qualities of emotion and desire. In this way, Elfen Lied shares much with the Alien franchise; just as, in a series of freak accidents motivated only by chance, the simple freighter crew-woman Ripley is inexorably tied to the grotesque Xenomorph race, so Kouta is enveloped in a bizarre government project as the result of his emotions and libido.
In this series were a few majorly tear-jerking moments that rank among my favorite in television and cinema. A line of dialogue that has been received quite favorably is Lucy's "Kouta, you were but a passing dream I could barely see in this hell." I was profoundly touched to hear that. It has the same staying power as some of the greatest lines in cinema, up there with "Forget it, Jake. It's Chinatown," and "No, I am your father."
Additionally, as has been mentioned by other reviewers, "Lillium" is a hell of a theme song, even though it's a bit overused within the series itself. And the opening animation is a little pretentious and silly, a mish-mash of Latin and Germanic themes as it is.
As aforementioned, Elfen Lied has a few pretty blatant plot holes. It's, sadly, not very convincing that Lucy became murderous because of being bullied as a child; the gravity of the response doesn't match that of the stimulus. If she was institutionalized because of the school incident, that would make more sense, but such a distinction isn't made in the anime proper. Also, the ecchi and male wish-fulfillment elements are rather pronounced, and could be distracting to someone not entirely convinced of the story.
I enjoyed Elfen Lied immensely and was willing to overlook some of its obvious flaws. The show is a hell of a tear-jerker.
