Josh Radnor...

My first response was to suggest that his performance in Mercy Street lacked a certain essence of authenticity, based mainly upon the cadence and tone within the delivery of his dialogue. Even though sarcasm isn't an invention of our time, his use of it here came off as far too modern in sensibility than what I would have imagined for a character in his position and time. Maybe all of this is the result of the direction he was given and not indicative of his instincts as an actor.
After a second viewing of the premiere episode, I'm less critically inclined. Perhaps I'm simply more curious and intrigued with how the story is being told and becoming more inclined to suspend disbelief.