The main point of interest in this classic is the fact that it was a first. The introduction is more interesting than the book in many ways, putting it in its context and explaining why it was significant. The introduction is short, don’t get me wrong, but the story itself is a fairly typical one in many ways. You can guess at the motives, and the mysteriousness is not at all mysterious to someone used to the genre. Not that it’s bad, just that it’s not particularly unique or surprising in any way. The writing is workmanlike, and in some places dips into being almost incomprehensible (but then, I find Dickens like that at his worst, and some people think he writes amazing prose, so take me with a pinch of salt). The plot probably was rather shocking at the time, but leaves me going, so? And of course, the poisoning by proxy is rather… impossible.
In any case, I had fun reading it in terms of connecting the dots with other classics of crime fiction, and it wasn’t a bad way to pass the time, but it’s not something I’m wildly enthusiastic about or would particularly recommend.