We go here from time to time. It's not going to blow your mind, but I do think it's probably the most authentically French restaurant in all of Boston. Authentic in the sense that it actually feels like many of the small bistros I frequented when I lived in both Paris and Provence.
I think what I appreciate about Pierrot is how they're not trying to be anything. They just are. So many restaurants in the Boston area go to great lengths to capture the spirit of the "French Bistro" (Whatever that term means anymore) but Pierrot succeeds because it is a reasonably priced place to get the classics. If anything it's boring, which is kind of what I like about it. It's like going to a diner in America. You need places like this in your rotation in the same way you need diners in your rotation or nostalgic places.
It's been at least six months since we've been but I seem to recall enjoying a soupe de poisson special with rouille, their magret de canard, and the Onion soup. Nothing crazy on the wine list but it covers the bases and is reasonably priced especially with the carafes. Service is French style (efficient, professional, perhaps slow or cold to some).
Although I like the feel of this place though, with Eastern Standards prices, cocktails/interesting wine list, and exceptional service, we find ourselves there more often than Pierrot (location isn't close to us either). ES doesn't take me back to France, but their food is more polished and I prefer their steak tartare and Salade Nicoise. You could spend more and hit Hammersley's or Craigie (and have mind blowing food) as both are considered Bistros but both of those are sort of stretching the word. All in all Pierrot is worth trying with the right expectations: A place with reasonable prices, French classics, and without pretense. It's probably most comparable to La Voile although a touch cheaper and I'd prefer Pierrot.