First off, I love Dollhouse. It's one of my favorite shows. It asks some great questions about the world and the nature of humanity. It has to go to some very nasty places to do so. Places I'd never take a kid.
The one place where Dollhouse wins is feminist messages. Its full of strong woman with varying degrees of strength and empowerment, though in the end it seems like men call the shots way too often--then again, the show is partly an indictment of the objectification of women, so showing the horrors of that works. But the truth is that Dollhouse is a series for adults, and its objectionable content and complex moral dilemmas are hard for teens. Out and out evil characters end up being the good guys at various parts, the good characters do bad things, and groups of people with different ideas about how to save the world murder, manipulate, and even rape each other to win. Among all this are several mentally ill characters whose actions cannot be read as a moral judgement, yet who spout delusions of morality. It's a complicated landscape of ethics that a young teen probably can't navigate, and some older teens couldn't without help. Some of the content in this show was so horrific that I cried, screamed, looked away, and I'm a 23-year-old woman who's been laughing at horror movies since I was half that age. I think this is just too much for younger teens. Definitely watch as a family with your older ones. You might need your older teens' wide-eyed idealism to process the terrible things they do to Echo.