Thoughts on MW Craven’s Washington Poe series?

No spoilers, at least not intentionally. I like to read but I'm not an expert or a critic, just got to musing about this.

Just finished the fourth of the series, and it got me thinking. The structure and overall plot was "fine", intricate, surprising, twisty/turny. But, looking back at my notes-to-self on Goodreads:

#1 – five stars; loved the characters, graphic crime details, story arc, and wrapup.

#2 – five stars again; returning to familiar characters and setting, but fleshing it out with a grisly mystery that wound all over the place without quite crossing into implausibility.

#3 – three stars; the overarching plot device (though apparently real per the endnotes) didn't get enough attention and the whodunit was frankly pretty implausible. Structure and characters still fun, but fell quite short.

#4 – three stars here too. What got me, and the reason for my post, was the almost mechanical structure to the plot. Not quite a deus ex machina / Chekov's gun overload, but seemed like a puzzle that every piece fit too neatly. Though it was an interesting read, there was very little in the way of distraction or development of the returning characters even Poe's house as a recurring theme was used as a plot piece, which I found overwrought. Also missed the grittiness of it. Yes there's violence and murder, but it was pretty deep background, particularly when compared to #1.

So, this is what got me thinking (dangerous at the best of times) – do you suppose I'm looking for more meat on the bones? IE more Agatha Christie nattering over scones (for worldbuilding and red herrings)? Or maybe the lack of in-your-face horror is the missing flavor? Just curious, I suppose, since Goodreads likes them all about the same. If I'd read #4 first, I'd not have read any others, that's for sure.