Christoph Scheerer (nee Wisnewski)'s book on the Blackmar-Diemer Gambit is a much-needed attempt to provoke some objective and serious discussion and analysis of the merits of the Blackmar-Diemer. For many years, the Blackmar-Diemer has been embraced enthusiastically by some players at club level and in correspondence games (sometimes to the point of obsession, trying to get it in every game). In the meantime many masters have dismissed the Blackmar-Diemer mainly with scorn and neglect, refusing to give it much attention in openings books, and tarring all Blackmar-Diemer fans with the same brush as the obsessive ones (ignoring the possibility that the Blackmar-Diemer might well be no worse objectively than its more respected mirror-image, the Goring Gambit).
Unlike most "Everyman Chess" books, Scheerer uses the "analytical tree" format rather than the "complete annotated games" format- I personally prefer this format in openings books, as it makes it easier to locate the lines you're looking for and makes it less likely that important lines will be missed out. The book is pretty epic at 336 pages- although Scheerer claims that it isn't meant to be a comprehensive coverage of all Blackmar-Diemer lines, it is pretty close. Much of the analysis is of high quality, with reasonable assessments, and Scheerer makes a strong case for the gambit being a viable way to reach dynamically equal positions which offer attractive tactical possibilities to the creative and attacking player, though not promising White a theoretical advantage.
There are various lines where White's traditional 0-0, Qe1-h4 approaches are shown to come up short, and slower (but not necessarily any less dangerous) build-ups including queenside castling are shown to be more effective, most notably against the line 1.d4 d5 2.e4 dxe4 3.Nc3 Nf6 4.f3 exf3 5.Nxf3 g6. I don't think his suggested lines in the Alchemy Variation (5...c6 6.Bc4 Bf5 7.0-0 e6 8.Ng5 Bg6 etc) quite work out for White, though as he mentions early in that chapter White does have a promising alternative in Lev Gutman's 7.Bg5 e6 8.Nh4!?.
Why 4 stars instead of 5? Some parts of the book are "analysis-heavy", which means that the book probably isn't suitable as an introduction to the Blackmar-Diemer for novices (you probably need to be about 1600 Elo upwards to benefit from the book). Scheerer quotes large numbers of low-quality internet games, sometimes basing his assessments on the positions that result around moves 10-15, which is understandable as there haven't been many top-level games in the Blackmar-Diemer, but it does bring question marks over the accuracy of some of the analysis.
But the book certainly does succeed in its overall aim of stimulating objective debate on the Blackmar-Diemer, and for advanced club players it is a very good source on the ins and outs of the various lines of the Blackmar-Diemer complex.