The unfinished exterior is an aborted Michelangelo project to be done in Carrara marble in 1518. Though Michelangelo did complete the internal facade, viewed from the nave while looking back toward the entrance.
Design and construction of the church, starting and stopping from 1419 through the 1490s, was overseen by several individuals, starting with Filippo Brunelleschi (of Duomo fame), the results of which strayed significantly from the original plan. The chapels in the transept are the only part of the building known to have been designed by Brunelleschi.
Notable artworks include Fra Filippo Lippi’s Annunciation and Rosso Fiorentino’s Sposalizio della Vergine.
The Old Sacristy (Sagrestia Vecchia) was done by Brunelleschi, with adornments by Donatello.
The adjacent Medicean Chapels, with gorgeous tombs sculpted by Michelangelo, have divergent hours from the church. Time your visit carefully to catch both sites.