The only reason I gave it four stars is that I'm not into plays very much. Still I realize that the book is one of the greatest of its time with loads of genuinely funny dialogs and monologues and effervescent jokes.
The action takes place on the eve of World War I. And as it had been previously mentioned "lampoons British society as it blithely sinks towards disaster". Somehow I don't quite agree with that. Even though the story deals with Britain and the British, the whole situation, the relationships between those people can be projected into other countries and cultures as well. The author wanted to point out the ignorance and indifference showed by the upper class to the World War I and its consequences. The main issues of the play are self-indulgence and lack of understanding of the high-class characters. I guess it's true for most other countries. The rich lived not noticing what was happening around. This fact has led to many conflicts throughout the history.
Apart from animate characters there is an inanimate one, that is the House which is often called the Ship in the play. The ship must be guided properly by sane people, the same stands for the society. It's an interesting metaphor. It's not new though. The ship of state is a famous metaphor put by Plato. It implies that the steering of a ship is just like any other "craft" or profession - in particular, that of a politician.
The book is definitely worth reading, it gives a lot of food for thought.