I rather enjoyed Arcadia, so when Caroline saw this, she got me a copy. Arcadia was very '90s, fractals and the like. This is much earlier, and Stoppard was clearly influenced by Beckett - very existentialist and all that. It does, however, have a Stoppard feel to it - stylistic similarities to Arcadia those decades later.
The plot concerns the minor characters from Hamlet, Rosencrantz and Guildenstern. Here, they become the focus of a play, but they are still bit players - things happen to them that they don't understand as the plot revolves just out of reach. The running joke is that no-one can really remember which is which (including themselves). They seem to have burst into existence purely for the purpose of Hamlet, and are confused by this.
There are themes. Death is clearly a major one, and plenty of existential confusion and absurdity, so it's not exactly light work. Chance, fate and destiny are there. There's actors and plays within plays (the idea from Hamlet pulled out into something much richer). Lots of interconnected bits and pieces, some more obvious than others.
In short, this is good, and a play I wouldn't mind watching, though not as much as Arcadia. It doesn't have the effortless flow of the other, but there's still the feel of a complex little puzzle.