Despite its flaws, this is a very satisfying book. The language seems dated to modern readers, but that is a minor matter, and has its own quaint charm. Dr. Kennedy, the protagonist, is a prime example of the "scientific" detective, a Sherlock Holmes with gadgets, and there is little, if any attempt at character development. There are also stereotypes prevalent at the time the book was written. All the women are young and beautiful, especially the criminals, and the heroines are also sweet, plucky, and innocent. There are ethnic stereotypes, too, but nothing offensive.
The things I liked about the book were the breadth of crimes, everything from murder to political blackmail, and the variety of situations. The author can spin a good yarn. The dependence on scientific inventions (some of which I question) becomes a bit tiring, after a while, but I suspect these stories may have been published separately in various places, so the reader wouldn't have been subjected to tale after tale with the same method of resolution. In addition, such stories are the progenitors of those we enjoy, such as all the incarnations of CSI, NCIS and other forensic TV shows and books.
I recommend this book, but I do suggest reading a story or 2, then reading a bit of something else, and returning for another small dose.