I hope all you mystery readers appreciate the work we writers put into killing people.
For me, a plot has to make sense, be satisfying, and follow logically. I try very hard to avoid TSTL moments (too stupid to live) where a character goes after the killer alone, at night, in a swamp, in high heels or whatever.
I want my readers to have a fair shot at identifying the killer, but I really hope they are surprised, too. In the book I finished reading this morning at breakfast, the clumsy cop who got in the way of the investigation was just a bit too inept for believability, and I knew he was The Guy.
Of course there have to be red herrings (NPI), not too many, though. And when there is a scene where the killer spills his/her guts to the protag, I require a really good reason for them to be spending time together, not just a desire to gloat on the criminal's part.
The denouement, the "unraveling", should be evident by the time we get to it. There should not be long scenes where the sleuth explains motivation or complicated factors. Hints interspersed in the story should come together, so the reader thinks, "I should have seen it coming."
What all this does is make it difficult to write a good mystery. I would never claim that I'm great at all these things, but it is what a mystery writer should strive for: logic and believability, with an ending that wraps everything in a package that makes the reader say, "That's good."