The premise is the organization called "the dollhouse" contracts young people for five years of their lives, in which their personalities and pretty much all of their non-essential mind is erased. The Dollhouse can then implant the person with any personality they want. The dollhouse uses this to serve people; lame examples off the top of my head being if you want someone to help you solve a murder, they can imprint a "doll" with the skills to do that. If you want a perfect date with someone who is 100% compatible with you, they can imprint a doll with that. And unlike the matrix where Neo's all like "I know kung fu," the dolls that get imprinted believe they're who they're made to be. So when a doll gets imprinted, they believe they have been the person they just got made to be, their whole life.
The cool thing about it is it starts with some very interesting yet very reasonable missions, and as the first season progressed, what they did with these dolls became a little less scrupulous. I don't often find myself in conflict with TV shows, but by the end I couldn't tell if I agreed with what the Dollhouse was doing or not.
A lot of cool shit happens, I'd reccommend watching the first season because its awesome. The acting isn't always Emmy-worthy but its pretty good overall, and the mental debates that come from it are incredibly interesting.
What I heard is while it did very poorly on television, it did very well in digital downloads and other avenues, which is how it got renewed. But yes, it is the lowest rated show to ever get renewed, which if anything shows despite a small audience it has something to bring to the table.