Una could be the sequel to Lolita, only in a different universe. This is every bit an indie drama: it deals with taboo subject matter, it's slow, it's 99% dialog, and it doesn't have a satisfying ending.
The movie is an adaptation of a stage play - Blackbird. Having never seen the play, I can't compare the two, yet the movie has the confined feeling of a play, since it mostly takes place in one location.
Here is where I think the movie really suffers: Una - our titular character - confronting Ray at work - while he's working - forces the story into two directions; the plot thread of Ray's work life keeps derailing his story with Una - much in the same way Una was shoving her issues into Ray's day. Two movies for the price of one? Uh, not really. I didn't care about Ray's work like. The movie is titled Una, we follow Una, it's her story, I want to see that. Just the thought that this interaction could have been set anywhere else, where the two characters could talk without being interrupted would have resulted in a better film overall. I love Rooney Mara's movies, and I could watch her in anything - especially when she has nude scenes, like here. The movie has much to say, and it's sad that it never gets a chance to really say it. There are several films that touch on this subject - statutory rape, to put it in legal terms - but this is the only one I have seen that asks what happens in the aftermath, and years later.
So, yeah, an okay movie, but totally a missed opportunity. Una should have been challenging: asking tough questions, and not spoon-feeding easy answers.