I binge read the entire Lord John series in a few days of vacation (thank you grandparents for taking care of the little boy!), so they all kind of blend together. They were pretty well-written, per usual with Ms. Gabaldon, but I got the sense occasionally that she'd done a little too much immersive research in the time period and was out of touch with what a typical reader might know. (Kind of reminded me of Georgette Heyer's books getting mired in period slang.) 
 Additionally according to her website these books are stand alone and can be read in any order, but they definitely refer to prior events and are much better enjoyed in order. 
 I wouldn't have read these if I wasn't already attached to the characters thanks to Outlander, and I don't think crime/mystery is going to become my genre of choice any time soon.