Rosso Fiorentino (Red-headed Florentine), Giovanni Battista di Jacopo, was one of the greatest Mannerists, yet he's not held in as great a favor as many other painters of the Renaissance. I suppose there's a stylized fashion in his works that somehow repulses critics. Personally, I think he's incredibly original, and was one of the most obvious precursors of the sublimely wondrous El Greco. And what powerful softness he could create in an image as well, especially in his famous piece at the head of the post, Musician Angel.
Moses Defending the Daughters of Jethro
A Young Man
Madonna and Child with Putti