Here’s how Philip Schaff describes Melanchthon in a section of his history in which he compares him to Calvin:
Melanchthon was modest, gentle, sensitive, feminine, irenic, elastic, temporizing, always open to new light; Calvin, though by nature as modest, bashful, and irritable, was in principle and conviction firm, unyielding, fearless of consequences, and opposed to all compromises.
They differed also on minor points of doctrine and discipline. Melanchthon, from a conscientious love of truth and peace, and from regard for the demands of practical common sense, had independently changed his views on two important doctrines. He abandoned the Lutheran dogma of a corporal and ubiquitous presence in the eucharist, and approached the theory of Calvin; and he substituted for his earlier fatalistic view of a divine foreordination of evil as well as good the synergistic scheme which ascribes conversion to the co-operation of three causes: the Spirit of God, the Word of God, and the will of man. He conceded to man the freedom of either accepting or rejecting the Gospel salvation, yet without giving any merit to him for accepting the free gift; and on this point he dissented from Calvin’s more rigorous and logical system.
Melanchthon, to be sure, was of a gentle and sensitive spirit and he hated conflict. He hated it. But that hardly makes him ‘feminine’. Rather, he was simply practical. Students of history shouldn’t think for a moment of Melanchthon as a prancing princess. He just wasn’t.