The book has a very overtly German bias in terms of the events covered, but bemusingly is rather short on imperial constitutional politics, which, one would think, would be the primary area of interest for a German-focused account of the war. Wedgwood also tended to discuss things from the point of view of the anti-Habsburg powers, and some of the analysis is clouded significantly by the then-concurrent international protagonism of Nazi Germany (and the concomitant abhorrence of a centralized German state).
It's not quite a bare-bones account of the war, but it is awfully close; the things Wedgwood covered in the most detail - the Winter King, Mansfeld and Bethlen, the Edict of Restitution, the Swedish and Danish interventions, Wallenstein's death, and the IPO/IPM - are the ones for which the war is now, regrettably, known over and above all else. The pre-war constitutional problems and clashes got little play. The Dutch were practically ignored, while the minutest English involvement went under a microscope. Global consequences of the fighting did not show up. The French were mentioned for La Rochelle, Rocroi, and Lorraine but little else.
I mean, it's an okay book, but it definitely shows its age and there are much much much newer and better works out there.