The blatant anti-semitism was annoying, but hardly worse than the blatant racism we see in other books of the era, including one we'll be discussing next month. Or the blatant anti-feminism in so many. I don't condone it, but have learned to judge by the era, not by that specific problem. (Though I would readily admit that here the anti-semitism is specious, whereas racism is central to Passing.)
This is the first book from Sayers, and it is easily one of the two or three weakest of the Lord Peter books. And yet, even so, the humour of Peter's silly foppishness is very real and a delight, Bunter is already starting to be a force to be reckoned with, and the comparison to Jeeves is unmistakable. The difference here, however, is that unlike Wooster, Peter isn't a twit, though he plays one.
The Dowager Duchess is also a force to be reckoned with, and shows here unflappability and effectiveness here, even as she's a minor character.
One weakness, pointed out earlier here, is that Parker isn't well explained. We know from later books that he's a police inspector.
but while the clues are there to explain him, it's not well spelled out.