The Scapegoat is certainly a very curious novel. Its premise (two physically identical strangers met and change roles) is in no way believable. And Du Maurier's writing style can be described as elegent yet a bit dull. However for some inexplicable reason The Scapegoat is a memorable read; I found myself completely taken in by the story despite its silly premise.
To understand why, I think the answer lies beneath the surface of the story. After the two physically identical men switch roles, Du Maurier focuses attention on the lonely, nice professor who is suddenly forced into the role of a French landowner, businessman and ... cruel monster. It's fascinating how he pulls off not only the role reversal but digs into the twisted hearts of the people (spouse, family and friend) around him. I found the emotional, humane side of the story to be most compelling.
Bottom line: a ridiculous story made fascinating and memorable by the ever talented Ms. Du Maurier. However I fear the author's style in slowly building the story might turn people away before they reach page 50.