I love this painting. When I meditate on the First Joyful Mystery, this is the image that comes to mind.
… and (the angel) came to her and said, “Hail, full of grace, the Lord is with you!” But she was greatly troubled at the saying, and considered in her mind what sort of greeting this might be. And the angel said to her, “Do not be afraid, Mary, for you have found favor with God. And behold, you will conceive in your womb and bear a son, and you shall call his name Jesus.
He will be great, and will be called the Son of the Most High;
and the Lord God will give to him the throne of hsi father David,
and he will reign over the house of Jacob for ever;
and of his kingdom there will be no end.”And Mary said to the angel, “How can this be, since I have no husband?” …
And Mary said, “Behold, I am the handmaid of the Lord; let it be to me according to your word.” – Luke 1:26-38
Laura Lowder - One Woman's Thoughts 
I love that painting, too…
I first heard Fr. Benedict Groschel describe it on EWTN. His description was so wonderful I had to see if the Philadelphia Museum had it on-line. And they did! It must be one of their most requested works!
I love angels, and I am amazed that this painted over 100 years ago depicts Gabriel as it does. I had never seen an angel this way. On fire for God!