Short version: Lynn Shepherd has found her voice. The Solitary House is a confident of Bleak House that takes all the dark possibilities lurking behind Dickens' novel and pulls them forward to create a complex, intelligent mystery.
Full version plus a confession: The decomposing, maggot-ridden corpses of murdered babies ought to have informed me that The Solitary House was not my kind of book. I prefer my murders tidy and, consequently, lean toward the cozies. In consequence, though Shepherd kept me paying attention to the plot, I did end up skimming large portions of the book, so what follows is impressions of a rapid-reader, not a close-reader.
Shepherd really has found her voice. One of my major complaints about Murder at Mansfield Park, an earlier book (see my review here), is that she tried to sound too much like Austen, mining Austen's books and letters, creating a stilted novel that was neither one thing nor the other. The Solitary House sounds nothing like Dickens, and is all the better for it. Rather than attempting a straight retelling, Shepherd has taken Bleak House as something of a challenge and something of an inspiration. All of the darker possibilities that could be Bleak House (which is dark enough, in all truth) are teased forward and made an important part of the mystery(1). Tie-ins to other books (most notably Woman in White) also work much better here than in Shepherd's previous work.
Charles Maddox, something of a stick-figure in Murder at Mansfield Park comes much more into focus in The Solitary House as a driven, determined investigator . He has a complex relation with Bucket (from Bleak House) and a credible motivation both for taking the job and continuing it. Relationships here, in this book, are shown, and emerge as believable.
A note: Although I, personally, disliked the amount of gruesome detail in the book, I do not think it gratuitous. it belongs to the story Shepherd is telling and fits both the setting and the theme. She doesn't quite reach Dickensian heights, but it is a well-written mystery.
Recommended, though not for the squeamish.
For a review by someone who read and liked the whole thing, look here, at Fyreflye's Book Blog.
(1) Mild spoiler here:
Really, is any modern reader going to read Bleak House and not, at some point, take a look at Jarndyce's relationship with Esther and say "You thought what? When?