I finally saw Yen tonight and echo several of the comments already expressed in the thread. I feel it's hard to discuss this play without going into SPOILERS (this is due to the fact that act one is all about establishing atmosphere and the plot doesn't really kick into gear until act two)...
I think the play would benefit greatly with some cuts; an intermissionless presentation would be ideal, but if they insisted on maintaining a break in the action I think they should move it to after Bobbie goes off to commit the rape. That would also leave Hench on the floor, bleeding out from his head wounds and the fate of all three younger characters in limbo. Then cut to the next scene with Ari's mum character all dressed up and the audience left to piece together what happened. (At first I assumed incorrectly that they were at a funeral- Hench's- as I couldn't imagine any other reason she would get so dressed up. Then Hench enters, then you realize they're at a courthouse, etc. Makes for a much better act two opener.)
I did think the final scene between Bobbie and his mother was well acted, but ultimately unnecessary. Despite Bobbie being neglected and understanding that he was dealing with serious psychological issues, I didn't really feel much sympathy for him. The juvenile detention center actually seemed to be the healthiest environment he had been in, so I didn't really understand the point of including that final bit. It would have been more realistic to end with Hench and Jenny in the park, IMO.
I did enjoy the acting a lot; Graynor's accent felt a little off at first, but the other three did solid accent work. Trip Cullman, once again, brought some strong direction to the piece.
All in all I think it was worthwhile to see Yen.
Marie: Don't be in such a hurry about that pretty little chippy in Frisco.
Tony: Eh, she's a no chip!