Okay - "Man on the Street" was a very good episode, and the first to give me hope for the series as a whole. Many spoilers ahead for those who haven't seen the episode yet.
The ideas the episode explores are grounded in characters and relationships rather than in a bad, philosophy 101-esque allegory - in particular, I think this episode offered some thoughtful exploration of the question of whether or not people ever genuinely connect with/love one another or whether they just love/connect with what they want people to be. Pretty much any of the developing relationships on the show toyed with this issue in one way or another, with the romance between Ballard and Mellie being the most obvious.
Through the assignment in which Echo is engaged at the start of the show, the episode also invites consideration of fantasy, and whether or not there's any such thing as an innocent or victimless fantasy - and thank god the episode didn't offer a preachy answer at the end.
Plot-wise, the reveal of Mellie as a doll (it was obvious she was a doll) was much better than I thought it would be - first, Adelle pretending that Mellie was a normal civilian cast doubt on what seemed to me to be Mellie's obvious status as a doll, which made the reveal of Mellie as a doll more exciting than it otherwise would have been. Additionally, because Mellie had been set up at the start of the episode as the "real girl" that Ballard is missing out on as he pursues Caroline, it's satisfying to see that in reality, she's no more real than Caroline, which calls into question the very categories of fantasy and reality. Whedon did the same trick with the categories of "good" and "evil" in Buffy and Angel, and if Dollhouse also turns out to be a meditation on power, I won't be disappointed.
That an FBI agent would trust, shag, and confide in his pasta-baking neighbor all in one episode we shall overlook and forgive in light of the strength of the episode as a whole.
Finally, in terms of the potential of the series to go somewhere interesting with both plot and characters, it is excellent that we can't know if the "person on the inside" is an actual person, Adelle's creation, or Caroline/the emergent Echo herself. That is quite interesting - much more interesting than Alpha, though it's good to have him/it in the mix, too. The idea that the DollhouseS could have some larger purpose also has potential.
And of course, finally, the fact that this was actually a true ensemble episode helped it along a lot. Hope that trend continues.
For the first time since the series started, I am interested to see what happens next week.