Perhaps it's ungracious to start by saying that like many I consider the attribution of this setting of the Magnificat to Pergolesi to be more than somewhat dubious. I think on stylistic grounds that it's far more likely to have been composed by Pergolesi's teacher Francesco Durante (1684-1755). In a way it's not desperately important who composed it as this particular setting of the Magnificat has a wonderfully expressive simplicity that, when it's well sung, sounds as though it's very easy to sing but is in fact a very demanding piece of music for soloists, choir, and orchestra alike.
The superb quality of The Atlanta Boy Choir's performance in the video below gives no indication of the difficulties of the piece. The accompaniment which can often be overwhelmed by the chorus has been given its proper weight, the soloists are more than up to their task, and the choir respond magnificently to the text and to Fletcher Wolfe's conducting. If I have a quibble – and it is a quibble, I would have liked the tempo to be just a touch slower. But otherwise this is one of the best performances of the piece I've ever heard. Kudos to the Atlanta Boy Choir and their Alumni Men's Choir both for the performance and for making it on available on YouTube. The music video, performer information, text and translations all below the fold. Enjoy :-).