Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Since this is a play and each character speaks in his or her own voice, it's difficult to identify a consistent tone for the work. One thing does seem to be common about the way the characters talk: they're nearly all deeply interested in the world and their relation to it. Stoppard presents his cast of characters as a quirkily diverse bunch, but at the same time, he lets their enthusiasms shine through in every word, such that we can't help but get caught up in it.