The plot is complex, and although it is a tragedy (with a Hamlet-esque body count) that gets more and more grim with each passing scene, the dialogue, performances, and pacing make it hilarious. There is also the cognitive dissonance: normally we want two young lovers to be united against whatever odds they face; here we are reminded they are brother and sister, and it’s either immoral, unnatural, or just plain icky. One way or another, it’s compelling. Everyone turns in a great performance.