Controversial idea: A weak or bad plotter is not necessarily a bad crime writer.
Let me explain before throwing tomatoes. It has been my credo for years that a writer should be judged after what they tried to do rather than what the reviewer would like them to do. If a crime writer is not that interested in the subtleties of plotting or has other priorities then be it. I may not like or want to read their work but I won’t begrudge them for sloppy plotting since they never claimed to greatness in that department. Same for those who try but just aren’t very good at it – it doesn’t matter from a critical viewpoint as long as they’re aware of it and/or have other things to offer.
Is this to say that there is no such thing as a bad mystery writer? Not at all. Let’s take Carolyn Wells as an example. Her plotting is beyond sloppy, it’s downright awful – but it isn’t a bug, it’s a feature of her work. Wells obviously wasn’t aware of the issues with her plotting and her writing overall, and sincerely thought she was writing great or good detective stories. What’s more, there is nothing in her work that can be said to make up for her idiotic plotlines. We can thus proclaim her a bad crime writer, for the admittedly paradoxical reason that she wasn’t aware to be one.
Lest you think I’m disavowing traditional mysteries and joining the Dark Side of the Force, let me add that what goes for plot also goes for characterization. A writer like S.S. Van Dine for instance who made clear from the start that he cared nil about having plausible characters in his books can’t be faulted for that – it’s just part of his own approach to the genre, which you may like or not but must not be held against him. If on the other hand you proclaim yourself a heir to Ruth Rendell but can’t come up but with stock characters of the stockiest kind all the while being convinced you are a sound analyst of the human psyche, then I fear you may be a bad crime writer – and a bad writer in general.
Obviously this approach will have its discontents, hence me calling it a controversial idea. The crime fiction fandom is divided in two camps with on one side those I call the « puzzle purists » and on the other the « Literati » and both sides believe their own priorities are everything there is to the genre. I for one think trying to establish a single set of rules only amounts to impoverish crime fiction, a genre for which – sorry for the P.C. wording – diversity has always been a strength. To have, say, Dashiell Hammett, Cornell Woolrich or Anthony Berkeley – writers with very different personalities playing by different rules – is a plus, not something to be lamented.
At the Villa Rose 
I agree, though you’re still left without objective criteria for determining good or bad in either plotting or characterization.
J’aimeJ’aime
“The crime fiction fandom is divided in two camps with on one side those I call the « puzzle purists » and on the other the « Literati » and both sides believe their own priorities are everything there is to the genre.”
Well, yes, that’s sort of true, but there’s an important difference between the two camps. The puzzle purists confine their purism to their to-be-read pile and tend to be more open to the other side, while the Literati are much more evangelical in their views and much less forgiving. I personally don’t like Raymond Chandler, but you’ll never hear me say that man couldn’t write, because he could write circles around most of his contemporaries. Literati sees the traditional detective story as nothing more than a glorified game of clue and as outdated and obsolete as a punch card computer.
So it’s really them who are narrowing and impoverishing the genre, because my camp has no problem with Paul Halter, James Scott Byrnside and the shin honkaku writers exciting alongside Ruth Rendell, Elizabeth George and Scandinavian noir.
J’aimeJ’aime