This is a charming and fun play to be sure. Especially, this is fun if you have read or recently re-read Hamlet. What makes it fun in general is the kind of back and forth between formality and informality that the characters go through.
The premise of this play is that two relatively, but not entirely, minor characters in Hamlet are waiting in the wings of life for their various moments to show up to be on stage. It’s not that these are the actors playing the characters, but the characters themselves. Unlike a few other plays where something similar to this happens, we are not seeing characters directly responding to the idea of the play itself, but the characters responding to what is happening around.
If you recall, Rosencrantz and Guildenstern are the two courtiers, ostensibly friends of Hamlet, dispatched by Claudius to observe, to report, and to distract Hamlet in regards to his “madness”; Hamlet’s maybe act to pretend to be crazy in order to allow his machinations to stay hidden in plain sight.
And of course they do do this, as we see in Hamlet. But also, they spend their backstage lives bullshitting with each others the players, also stuck in a kind of caught-between state of use and ill-use.
There are several moments as the two play intersect and Rosencrantz and Guildenstern must immediately Be in Character and react and say their lines, and then come back to their lives. They even comment on it at one point, about the constant interruptions.