The easy parallel is to The Quiet American and there are quite a few similarities. They are both satires of Cold War adventurism and both aim to criticize western interference in other countries. However, Our Man in Havana is not nearly as scathing and it does not attempt to take sides in the way The Quiet American does.
The real them of Our Man in Havana is love. Womold is both motivated and haunted by his love for his teenage daughter and for the wife who left him. In fact, Wormold's scheme is an attempt to gain enough money to provide his daughter a better life. Later Wormold realizes he is in love with the Beatrice; the aid British intelligence sent to him. Beatrice gives the theme of the book when she tells the assembled military and intelligence chiefs that "a country is more a family than a Parliamentary system."
I always enjoy reading Greene and Our Man in Havana is a quick, enjoyable and fun read.