The film was mostly shot on location by veteran director John Huston. The shoot was a living hell, as Hepburn divulged in a later book. Bogart and Huston were mostly boozing and the others were plagued by dysentery.
The film, which was based on a 1935 novel by C.S. Forrester, is full of various "battles." First we have the battle between the Puritan intellectual and the unsavory, boozing captain. The Puritan wins: she throws the booze overboard and manages to persuade Charlie to prepare for an attack on a German gunboat. After they fall chastely in love, we have the battle with the old boat (Charlie has to manufacture a new screw and propeller without the proper tools) and the elements. There is a lot of sweat, but also pelting rain and swarms of mosquitoes and leeches. And finally we have the battle with the Germans. The attack on the German boat with homemade torpedoes misfires, but when Rose and Charlie are made prisoners and just about to be executed for their attack, the remains of Charlie's boat hit the gunboat and blow it up after all. Charlie and Rose swim to safety.
The problem of this classical film is with realism. The boat trip and the fighting relation between Charlie and Rose are very authentic, but the rug is pulled out from under the realist legs by some unbelievable coincidences in the script. The most blatant one is of course the blowing up of the German gunboat by chance... and by homemade torpedoes. Would they make even a dent in the hull? And where are Charlie and Rose swimming too, alone in the swamp-infested bush, without boat now?
There are also some filmic problems I found rather jarring. In an attack by mosquitoes, the insects have been projected over the scene, but they disappear in an unnatural way. Even worse, a spell of heavy rain has also been projected over the scene and here Huston has cut in some photography of wild beasts stampeding away. The "real Africa" of tourist posters, so to speak, but the problem is that in these unnecessary shots the rain has been projected over footage of animals running away in the bright sunlight! Sloppiness of a great director?
But Bogart and Hepburn keep us entertained. Hepburn was playing herself, as an American from the Puritanical Northeast, but Bogart had to play against type, he had to loose all his usual sophistication, wit and irony. We see him doing his best, although it is never completely natural. But he got the Oscar and not Hepburn.
What makes a lot good, too, is that we have a romance at middle-age here, a rare commodity on film.