I'm re-reading And Then There Were None (also known as Ten Little Indians and probably several other things) right now, for some reason, which is the first time I've read Agatha Christie since I was probably like twelve*. As I read it, remembering who the murderer is but not much else (and I probably didn't pick up on much else when I originally read it), it occurs to me that while Christie is a decent enough writer, and individual books of hers are entertaining enough, her real brilliance doesn't become apparent until you've read a wide selection of her works. Because she's relentlessly experimental with the mystery format, and that's, to me, really cool.
And Then There Were None, for those unfamiliar with it, is kind of the ultimate locked room mystery, but in real time: ten people are called to an isolated island on various pretexts, whereupon it is revealed that the person who summoned them believes them all to be guilty of a murder they're getting away with, and has taken it upon him or herself to punish them for it. One by one they are murdered, and they quickly realize that there can be no one hiding on the island, so the murderer must be one of them.
The cool thing is (in part) that it's obvious all along who the murderer must be. One of the characters is a judge, which kind of gives it away seeing as the murderer has to have access to a lot of judicial information on the various people and also, you know, sees himself as a judge. He is always made to seem unpleasant and inhuman(e), described as a reptile, and right from the start a bunch of the characters suspect him. He's also the only one who consistently has comfortable opportunity to do the murders.
But then (and here's the rest of the cool part) Christie kills him off about two thirds of the way through the book. You've spent all this time thinking, well, surely, he's the only possible culprit, but then he's dead and the murders keep happening! Of course, he has faked his death (I think--either that or he's set mechanisms in place that will kill everyone else off, I haven't gotten there yet and I can't quite remember), but that possibility just doesn't occur to you.
And a bunch of her other books fuck with mystery structure in similar ways. There's the one where the narrator did it, which is a brilliant idea, made more brilliant by the fact that the book also supports the interpretation that he may be lying to protect the real murderer. There's the one where the police detective called to investigate a murder at a house--who, that is, did not show up at the house so far as we know until after the murder was committed, and who does not at first seem to have any connection with the victim--turns out to be the murderer. There's the one where almost literally everyone is the murderer, even though there's only one murder. If I remember right there's also one where the real murderer is psychically inducing others to do the killing for him, but I think she was kind of senile when she wrote that one. Regardless, there are a bunch more along those lines, and that kind of experimentalism, especially coming in such genteel, classicist packaging, is very interesting to me.
In general I'm not that interested in mysteries as a genre, largely because most of those I've read (and I'm sure this will sound to a mystery fan the way someone saying science fiction is all busty broads being kidnapped by bug-eyed monsters would sound to me) seem more interested in quirks of setting than in the actual significance of gathering clues, solving things, and the process of investigation, which is what would be more interesting to me (and why I love Sherlock Holmes). And more interesting than that would be an investigation into the (I guess) metaphysical or philosophical implications of these things. Christie's experiments are a starting point for this, a gateway allowing it to be more fully explored in works by people like Jo Walton (the trilogy starting with Farthing), Michael Chabon (The Yiddish Policemen's Union), and Paul Auster (The New York Trilogy), among others, in all their extremely different ways.
By the way, if a real mystery fan comes across this and disagrees with my take on the genre, please, let me know. If my thinking the authors I mentioned were doing something new and exciting strikes you the way Phillip Roth saying "I had no literary models for reimagining the historical past" (idiot) strikes me, I'd love to know it, because I'd love there to be more works like this out there for me to investigate.
*Except I just realized I'm lying, because I read The Murder of Roger Ackroyd about four years ago after reading a critical essay about it, because I never had read it when I was in my Agatha Christie phase.