The first 15-16 episodes of the show were great....the rest wasn't. I wouldn't really call it full of fan service either, since that's more of an ecchi bullshit thing.....I'd call it mature. Chick kills herself in bathtub while taking a bath....she's obviously gonna be naked, people have sex....they show pretty much everything. If anything I like how the show portrays some sense of realism and how they they don't hide/censor anything. The story line got fucked up around 16 because the manga wasn't and still isn't finished, so they made up some shit and that's why nothing is explained. Heck just recently in the manga, they started explaining what gantz is.
Like other posters, I also find it interesting that you can like Elfen Lied and not this show for those reasons, especially the truly meaningless ecchi fanservice....and considering it's story is also weak IMO