I'm reading this at the moment and must say it's been superb so far. Its relevance to the Seven Years' War is (um...), well nil I suppose seeing as its about the Thirty Years War. Anyone with an interest in European history is certain to love this book though, IMO.
The wealth of information is immense and he places the war firmly in its historic context: trade relationships, industry, population, recruitment policies, logistics, taxation, constitutional arrangements, tactics etc all get detailed treatment. What was the volume of the Baltic grain trade at the time either in cash or in tonnage terms? How did the crown revenues of Denmark compare with those of the Habsburg behemoth? How much would a pair of top-of-the-range flintlock pistols, a sword, armour and a top quality charger set you back at the time? Answers to all these questions are provided.
Coming to the subject from a position of ignorance, I'm finding the book a fascinating introduction to early 17th Century European politics. The eternal struggles between crown, nobles, burghers and peasants are outlined for each of the combatants and I found much of the info very surprising.
Having had everything in the palms of their hands, the Habsburgs and the Ottomans lost focus and let it all slip away. Meanwhile the insignificant Dutch and Swedes were coming up with innovations in industry, commerce, social organisation and military affairs that would change the world.
The cast of characters is immense as might be imagined. Thankfully a comprehensive index helps with keeping track of everybody.