What do you see as the reason for the successes of the army of Gustav-Adolphus of Sweden?

We are talking about Sweden in the first third of the 17th century, Gustav II Adolf ruled from 1611 to 1632.

He fought with different countries and won all, he himself died in the battle of Lützen in 1632. The reasons for the success were as follows:

The war with Russia in 1610-1617 was quite easy for him, since the enemy was in trouble, that is, anarchy and the army acted weakly, so Gustav II Adolf managed for the first time in the history of Sweden to completely control the coast of the Gulf of Finland and the mouth of the Neva. This continued until 1703.
The war with Poland went on with varying success, but the Poles had a larger army.
His most famous victories were in the Thirty Years’ War in 1630-1632. His army was small, but professional, it consisted not of mercenaries, but of Swedish peasants. The weapons were of good quality and the discipline was strict.