Flawed, but I liked it!
I just finished watching this show straight through from beginning to end over a period of about a month, and to be honest, it had plenty of strengths and plenty of weaknesses.
Dushku, as has been noted by many reviewers here, was perhaps not the perfect actress for the main role. Near the end of season 2, I felt she began to seem more comfortable in her role, but at the beginning, she did very little for me.
On the other hand, Fran Kranz's performance as Topher Brink, for me, was the highlight of the show, especially in Epitaph One and Two - he starts out as a very simple character and takes on a good amount of subtlety by the end.
The show undergoes the transformation typical of a new idea finding its footing - the first half of season one played it safe and stuck to an easy, episodic structure. Then it started branching out, and there are some nice twists.
Honestly, where this show lacked, I felt, was in character depth. It gives you very little to latch onto until - very literally - the last episode, which for me at least was an emotional roller coaster. That episode alone, for me, justified watching the entire series. Echo has a breakdown at one point that by far constitutes Dushku's best acting in the series, and everything seemed to come together.
If you're looking for perfection, though, check out Firefly (or Buffy, which I have not personally seen but have heard amazing things about). Dollhouse has moments of brilliance, but I'll gladly admit I didn't like everything in it.
One last thing, and I do think it's important:
A review or two here described the show's premise as "depraved," some sort of sick fantasy involving brainless, willing sex slaves. If you're paying attention in the slightest, that's not what this show is about. Joss Whedon, if you're not familiar with his other work, specializes in creating settings in which no one is doing the right thing. Firefly is about a jerk of a captain, a smartass of a pilot, a hired gun, a prostitute, two fugitives and a lovesick engineer. There are no angels in his work; I think that's how he likes writing: Put someone in a despicable job, make them do despicable things, and find a way to show the audience something sympathetic through it all.
In this show, the sympathetic character starts as Paul Ballard, and eventually, as characters begin to realize the horrifying extent of what they're doing, Topher and several others become sympathetic as well. Even the colder characters - such as DeWitt - show moments of sympathy, even if they are ultimately not very likeable as characters, and when Echo starts to develop, she becomes fascinating as well, and also starts to put a new spin on things later on.
Personally, I recommend this show. But like anything on TV, in film, or anywhere else, it's up to you to decide for yourself. You may wholeheartedly disagree with everything I just said. You may think this show is the high point of human evolution, you may think this show is filth beyond the power of words to describe. Have fun deciding!