Many, perhaps most, deep readers would shrug at this.
It is the 21st Century now; this would have been hot stuff in the Centennial-dominated eighties or nineties. But the problem is that in large swaths of Civil War readership, it is still the "golden age" of ancient interpretation, and a backward readership needs to be tempted out of its caves and into the sunlight of new research and new thinking by shiny trifles that do not completely threaten all of the bad reading they have ever done.
I see this effect again and again. An author offers a breakthrough concept to a hidebound audience taking immense care not to upset them with too much novelty. There would be an insight in the center of the work and it would be surrounded by mounds of the same old same old. Newton's Joseph E. Johnston and the Defense of Richmond comes to mind. Massively revisionist in terms of Johnston, the author kowtows to every single cliche about every other general and incident. Revisionism was reserved for Johnston only.
Unholy Sabbath is exactly that kind of book. It reinforces everything that the low-information reader already "knows" while proposing a tweak to just one part of the consensus history. And maybe, politically, that's how you do it, without goring too many oxen and overturning too many apple carts.
But we're doing history here and history is our best attempt at the truth.
Here the malignant bungler McClellan accidentally achieves an outcome of import, through no virtue of his own. That is the sugar coating on the bitter pill of worthy victories.
RC Ocean gives books the "Young Napoleon" test. The higher the count of this usage in an ACW work, the less chance he will buy it. This book would fail his test.
Consider also these gems:
 Beyond a gross overestimation of enemy strength around Manassas, incessant carping, and criticism of the Administration, however, most of what McClellan offered was more bragadoccio.The Ocean test is fundamentally about polemics. Is the author a polemicist caught up in an emotional relationship with his material? If so, this is not history.
 With his right turned, McClellan ordered a retreat to the James River... 
 McClellan conveyed the news to his wife Ellen in his usual vainglorious style... 
[4} ... McClellan's caustic and predictable personality. 
 ... McClellan quickly began another round of of grousing ... 
 The general's acidic comments about McDowell and Pope continued, only inflating his already bloated ego. 
 ... Franklin proved to be as indolent and slothful as his sponsor George McClellan. 
... McClellan refused to recognize the extent to which Lee and his men were at *his* mercy. The Army of Northern Virginia fielded at most forty thousand men [upon crossing into Maryland]. 
Brian Matthew Jordan, in my view, set out to write a battle book. This is a narrative that seeks to fill a gap in publishing rolls where there should be a South Mountain campaign. Instead of being devoted to scholarly argument around the meaning and import of those battles, this is a story about marching and shooting. In Reese's Sealed with their Lives and in Harsh's books, the shooting and marching were constantly brought back to the commander's intent. The commander's intent is missing throughout here, the commander being an vainglorious imbecile. And so, "Stamp's conspicuous death sent a shiver of panic rippling through the men of the 76th New York..." Spare me.
In the parts where people are not shooting or marching, there is page upon page of generals' bios.
Jordan did not consult Beatie, Rafuse, or Harsh's Taken at the Flood (which last is unforgivable in a volume like this). He mentions Sounding the Shallows without resorting to its data tables. He gives lip service to Clemens' Carman without referring to Carman (did I miss a reference here?), and although a citation shows he has read everything Tim Reese published on Crampton's Gap, he completely fails to understand Reese's analysis of GBM's order to Franklin, Reese's analysis of the commander's intent for all the battles along the mountain, and Reese's case for the separation of Crampton's Gap from the South Mountain action.
Not that citations here are thin. There are a lot of them but they don't advance the cause. The working sources provide quotes and anecdotes; the rest seem to be window dressing.
Ultimately, the entire case for the unique value of the battles is made in one chapter running 18 pages filled with quotes and excerpts. It's as if the publisher asked for this addition. There is almost no analysis in that chapter; the "evidence" for the importance of these battles comes from the mouths of participants and contemporaries.
Jordan has virtues as a storyteller and will do well with his next book if he can limit the snide remarks, the emotional outbursts, and the big-picture stuff. He needs to really engage with the secondary sources, the controversies, and the implications of higher analysis.
On some level, this is an okay shoot-em-up, but who among advanced readers needs that?
Notes on the excerpts quoted above:
 I know of no first hand accounts of McClellan's carping, criticism, or bragadoccio. None. There should be some somewhere, but everyone who dealt with him found him to be kindly, courteous, attentive, and I would add concise, energetic, and at times, fun. Carping, etc. may be the author's readings of some notes found in the McClellan papers as rendered by Sears. They do not correlate to any wartime remembrances. Regarding strength around Manassas, McClellan passed through raw intelligence which he labeled as pass-through information. The Civil War author generally does not know the difference between intelligence and analysis, analysis being what produces an estimate.
 The sequence is wrong. It would have been a retreat if this sequence was correct. A change of base started before the battle began.
,,, This stream of vituperation seems to be based on Sears' renderings of notes found in the archives and do not correspond to any observed behavior of McClellan during the war.
 Franklin's sponsors were many starting with Salmon Chase, then Irvin McDowell, then McClellan, Banks, ultimately even Grant who tried to get him a command after the Red River campaign.
 That Lee crossed into Maryland with 40,000 men is not sourced. It is a remarkable contention worth its own book. The author has taken pains to avoid Fox, Livermore, Longstreet's writing on the subject, and Harsh's tabulations. He likewise avoids the testimony on enemy strength given Lincoln by the US corps commanders after the battle.