Vance is better at science fiction than he is at detective novels. SF allows more scope for his amazing use of language, and for description of the weird and strange. Despite that, in The House on Lily Street, Vance applies his skill to observation of ordinary humans. The result is highly credible and immersive study of human nature in all its foolishness and venality.
Structurally, the book works less well. After a gradual but intriguing setup, the last third of the book suddenly steps into higher gear as a chase and duel. The time frame shifts constantly and without good reason. It's not hard to follow, but it made me think that Vance just didn't spend much time editing; it feels more like a good draft than a polished novel.
All in all, readable, but only recommended for Vance completists.