Watching Miss Marple deal with her "helper" was fun. The plot was intriguing and the final solution well done. My main issue with the book was the police were told early on (and early in the book, so I'm not spoiling much) that the intended victim was probably not the one who died. But they didn't seem to acknowledge this until several chapters later! That irritated me a great deal as I read it. Other than that small issue, it was a good mystery.
It was interesting to read this one right after Body in the Library. Time-wise the two are very separated--Miss Marple is much older and the house has changed owners several times. But they both had bodies in the same house, and there were references in the gossip-mongering about the old one. Nothing that was needed for this mystery, just some atmosphere.