Most of the reviews I've read for the premiere, 'Vows', haven't really mentioned Jamie beyond being a guest star, but HollywoodChicago.com chose to bestow some compliments on his performance.
And not related to Dollhouse, but Bear McCreary, in his most recent blog post, discusses his work on the new series, Trauma, and conducts a brief interview with Anastasia Griffith, Jamie's sister in which she talks a bit about her brother. Bear also, amusingly, recounts how he didn't realize Anastasia was Jamie's sister while initially scoring the pilot.
ETA:
The Televisionary thinks Jamie is "fantastic" in his role.
Bamber is fantastic as Martin Klar, a wealthy financier who weds Echo but whose business is just a front for international arms trading. It's a nice change of pace to see Bamber portray a villain for a change (and with his native British accent as well!) and he carries off the role with aplomb.
IF Magazine mentions Jamie's "lively guest turn" as a high point of the episode.
