Some of them are great--you can't go wrong with Shep Paine's. His books were my own modeling manuals that taught me the basics and instilled good modeling fundamentals. Shep wrote to teach and to educate -- other books that I have seen., however, seem to be more "vanity showcases" for an individual modeler, with little actual clear technique or descriptive photography. Some of the Osprey modeling manuals are this way--lots of highly complex models and often scratch building skills that are just out of the range of the great majority of modelers. A Panzer IV modeling manual comes to mind where the interiors and other incredibly intricate details of some of the models were just mind boggling in complexity. I looked through it and felt defeated rather than inspired.
Mike Rinaldi's book on German armor is well done. It has some valuable advanced finishing advice.
This same standard is also seen in some of the "how to" guitar videos out there, by the way. Some of them are very deliberately produced with the idea of actually teaching and showing novices how to improve. Other players simply use them as a sort of egocentric display of their abilities--rather like "betcha can't play THIS!". Such productions, whether video or book format, are of use to few but the actual author for purposes of braggadocio.