The tone of this play is the product of its narrator. Because Tom tells us about the play by looking back from a rather sad state, the scenes are necessarily imbued with narrator Tom’s emotions. He regrets having abandoned Laura, so all the scenes are filled with a sense of regret. As for the metafictional stuff, we mean the dramatic music at key moments, the screen projecting images, the general way that we the audience are never allowed to forget that we are watching a play. There’s also Tom’s introductory speech, where he make reference to the play you are about to see. That’s meta-fiction, or, in this case, meta-drama.