Hate to say it, but Eliza Dushku was the weakest part of the show.
I was re-watching some episodes of this wonderful show and the majority of the cast were just phenomenal - Fran Kranz, Olivia Williams, and especially Enver Gjokaj really turned in some great performances every episode, but Echo was the main character, and while Eliza wasn't bad by any means, she just seemed very..."plain vanilla" compared to the other actors. She was tolerable, but I felt like she never really delivered on the diversity of the different "imprints" that she was supposed to be portraying.
I've been watching the show Orphan Black from its beginning a few years ago, and I can't help but think that someone like Tatiana Maslany could have really taken the Echo role to another level, with her ability to transform herself into completely different characters so convincingly that I forget that I'm watching the same actress portraying all of the clones every single episode.
Just thinking out loud, and if you liked Dollhouse and haven't checked out Orphan Black, do yourself a favor and start watching!