I cannot directly comment on Tagg's observation that Vol. 1 is "idiosyncratic," as that is subjective to each reader. Some will like Cap's style and presentation (it is very old school and proper), and others will not. I can indeed confirm that Cap has spent more than three decades on this project, has found reams of material no one else has used or has used very selectively, and it is my opinion that the series will transform how serious scholars look at the AOP in general, and McClellan in particular. It will be many volumes, though the latter ones should cover more territory that the first 3-4 because Cap believes it is important to deeply examine the early foundation of the army, which has essentially been ignored or misunderstood for far too long.
Savas on Beatie
In my recent Beatie post, I forgot to include these interesting public remarks on Army of the Potomac by publisher Theodore Savas. He's replying to observations by ACW writer Larry Tagg. "Cap" is Russel Beatie: