I'm going to go against the grain here. Now, I really love the work of Stephen Sondheim. Since my first experience with Sweeney Todd, his art has continued to surprise me. However, this play was possible his worst and I can see why it failed to find popular audience.
In my opinion, this play sent out a terrible message to the audience. From personal experience, I realize how dangerous obsessive love can be. There is nothing romantic or passionate about obsession and the behavior Fosca presents. The entire romance is just plain frightening and creepy. Fosca would have been more sympathetic if she had suffered from unrequited love alone rather than obsession.
Marin Mazzie (Clara) gives the strongest performance in this, and is the only thing I enjoyed about the play. Some of the music is nice, but definitely not Sondheim's best. The sets and costumes are rather boring as well. If you're looking from some good old Sondheim than I would suggest watching Sweeney Todd, Into the Woods, West Side Story, and Sunday in the Park with George. The music, appeal, and overall production is so much greater in those plays.
