Firstly Quarton's work is a painting whereas Michelangelo's is a
sculpture.
This means a very definite difference in expression.
Secondly Michelangelo concentrates on the Virgin as she is
holding her dead son.
Quarton shows the donor contemplating a group, consisting of the
Virgin, The dead Christ, John the apostle and Mary Magdalene. A
background landscape and city are barely visible.