Caravaggio's Mary is depicted in a devout kneeling pose, the viewer can see she has accepted the part that God has chosen for her and is willing to receive the Holy Ghost. This in in contrast to for example El Grecos depiction he shows he in a state of shock with her hands raised to her breast. Many artists would paint the annunciation in oppulent surroundings, but not Caravaggio, he has painted Mary in dark surroundings if the viewer looks closely a chair can be seen and a bed, but all the attention is focused on the angel and her face, as if Caravaggio is conveying the message that this is what is important, Mary and the angel, not the surroundings.

The Annunciation
El Greco