Very good; would be interesting to produce. I hesitate to say this because I'm not nearly enough of a mathematician (or whatever it involves), but Stoppard seems to me to be playing with Heisenberg's uncertainty principle, doing as much as he can give us the feeling of watching it work. A cat's life isn't at stake, but he does a lot of sending two characters into an unseen space (and otherwise obscuring them), and making us guess which one of the two we're seeing. Or which came out. Because I've read too many mysteries, the plot and its solution are not particularly compelling to me--or perhaps it's because the characters are not terribly compelling in themselves. What makes the play worth reading is its work with its underlying ideas, and its ability therefore to make us work with them. But maybe I should re-read it.
Most writers have a strength, or two, or three, and you can't ask them to be all the things that literature (and drama) give you as a whole. Thus with Stoppard. I really enjoy him, even when his characters aren't at the level of Shakespeare or Boll.