This question may be too broad, but if that can be answered it'd be nice. I'll try to narrow it down;
How did Adolphus Gustavus fight against the armies of Poland and Muscovy (later Russia)? By this I don't mean their levies or mercenaries, but rather their cavalry traditions. Both nations are particularly known for creating the light cavalry, which was later adopted by the West, but how did Gustavus combat the professional cavalry?
I recall reading that Gustavus created the modern dragoon, and made them into general workhorses (engineers and sappers), how did this work? Were they simply mounted engineers who knew how to use a gun?
Was the combined arms approach of his armies. How did he come to have his cavalry function as artillerymen, artillerymen as infantry, etc.? And how? I'd imagine this exponentially increased the cost of his army, and the time it'd take to recruit and move them.
And finally, what were tactics that are often attributed to him? I know that he believed "Raitar" should dispel a volley at close range before a charge, but didn't "Cuirassiers" already do this? So why is it attributed to him, was he simply the first to make it the norm?
Until Gustavus, the Spanish had a legendary formation called the Tercio. Essentially a square loaded with musketeers and pikemen that could repel almost any attack. I can't recall what the name of the Swedish formation was, but im pretty sure it was developed by Gustavus during or before the Thirty years war and it was very successful against the Spanish Tercio, which explains the Swedish dominance throughout the Thirty years war.