To be fair if you know what Stross's Laundry Files books are about you'll realise that both the books and that cover are intended to be spoofs. Spoofs of spy novels and spoofs of Lovecraftian style horrors. In that sense that cover suits the books perfectly. It is meant to be corny and cliched right done to the girl's pose and glasses.I love great SF art on book jackets. But I would rather read a book with no art than bad art.
Based on the cover, I wouldn't read this: