The story is a mess, the characters are really stupid, you can't really watch it without raging from minute to minute.
Unless you can enjoy the gorefest shutting off your brain, Elfen Lied isn't really recomended to anyone.
The manga is even worse.
Considering the nature of the story and its aim for gore fest entertainemnt, I thought the story was decent enough to hold ones attention, especially since the chracters are stupid. Also Its short enough for the show, not to have a deep meaningful story, so its easier to go along with its stupidity whilst having fun.
Its a dumb Anime, but I do think there is some redeeming quality about it that deem a recomendation for people who doesn't have any expectation (when told about it)