Ryckman's book is an excellent work full of novel insights. Ryckman single-handedly revives the non-positivist "transcendental philosophy" insights of early discussions of General Relativity Theory. Much of this suggestive insight and interpretation was lost with the triumph of the logical positivist (later logical empiricist) appropriation of Einstein's relativity theory as showing that Kant's a priori and transcendental philosophy was overthrown by Einstein. Schlick and later Hans Reichenbach became the "standard" interpreters of General Relativity Theory by the end of the 1930s. Later American philosophers of science, such as Adolph Gruenbaum and Wesley Salmon, even where not agreeing with all claims of Reichenbach, very much followed his lead and tended to dismiss the neo-Kantian and phenomenological interpretations that were developed by European thinkers concerning relativity theory.
Ryckman discusses the work on unified field theories of mathematician Herman Weyl and the physicist Arthur Eddington, as well as the philosophical interpretations of general relativity by Ernst Cassirer and Emile Meyerson among others. Ryckman's grasp of both Husserl's phenomenology and of the relevant differential geometry is superb.
His long sections on Herman Weyl are tremendously informative and illuminating. I think Ryckman's interpretations of Eddington as a "transcendental philosopher" in the traditional sense of Kant and Husserl are a bit of a stretch, however, as Eddington's philosophical excursions were very much seat of the pants. Nevertheless Ryckman persuasively discredits those, like Susan Stebbing, who ridiculed Eddington's philosophical interpretations without understanding the physics and mathematics that led him to them.
A minor but significant weakness is Ryckman's totally downplaying and dismissing the influence of the German romantic idealist Fichte on Weyl's interpretation of field theory and matter, claiming that Weyl was interested only in Fichte religious thought. In fact Erhard Scholz has made a well documented case in various articles that not only Husserl but Fichte was a very strong influence on Weyl's interpretations, and Weyl says so himself in his autobiographical reminiscences.
Overall Ryckman's work is an outstanding contribution and I hope it will revive interest in phenomenological philosophy of physics among physicists as well as Anglo-American philosophers.