I've read either little or no Allingham (I can't remember if I have) and now feel strongly tempted to.

I love the Campion books: they are one of my favorite Golden Age series. I read them straight through in order, but I have begun to recommend starting with The Crime at Black Dudley (1929) so as to see Campion as discovered by his creator, a scene-stealing minor player whom she shortly realized was running away with the plot from the ostensible protagonist, and then skipping forward to Sweet Danger (1933), which is the one ethelmay mentions where Campion himself and the kind of series he's in really crystallize, perhaps not coincidentally introducing the excellent romantic heroine. You can always return for the intervening novels if you feel like observing the evolution of Campion from a Wimsey file-off to his own individual person, although since last summer's re-read I am trying to remember that Police at the Funeral (1931) is the one which has a degree of racism baked into the plot which I consider out of Allingham's period-typical norm and frankly book-destroying for me. The Fashion in Shrouds (1938) requires a similar heads-up for its density of gender nonsense—I characterized it recently to sholio as heteroaaaaargh—except where Campion and Amanda are concerned, which is a good thing because its events entail a crucial stage in their romance, which results eventually in what I consider one of the great marriages of detective fiction. (He's . . . actually his profession is difficult to categorize, but it always involves looking into things. She's an aeronautical engineer. Together they really do fight crime, usually because crime started it.) Allingham ran the series in real time until she died in 1966, so one of the pleasures of the books is getting to watch everyone grow and change and their world which is perhaps not exactly ours change around them. One of the others is the aforementioned range of genres on offer, all with some element of crime or detection but otherwise take your pick: some are cozies, some are adventures, some are noirs, at least one qualifies as a novel of romantic suspense, another is plain screwball, there's a generational drama, I haven't even mentioned the Dick Francis-type feature where most of the books cluster around a different interest or milieu, and then we have the science fiction which provoked this entire post. Generally speaking the earlier novels are more formally conventional, the later ones can be much more experimental. The characteristics that make a "Campion novel" are not a formula. I can't really think of another series like it from its time. I like Allingham's prose besides.