A CD jacket I have for his Stabat Mater says it was the single most popular piece of music in the eighteenth century. I don't know whether that was correct or not, but the music is superb. I have three or four versions of the Stabat Mater. The version I enjoy most is the one with Margaret Mitchell. A bit slow for some, but well done.
If you are interested in other Pergolesi music I'd recommend his Missa Romana in an Orfeo recording with Roschmann et al. I see it is still listed in Amazon with online playable excerpts. Listen to the finale (track 8). Joyous music. My wife wants that finale to be played at her funeral along with Mozart's Queen of the Night aria.
Both are what I call ‘haunting’ music - I just remember those two girls playing Sabat Mater on the sidewalk .... then I bought the CD ...