I’ve listened to this piece 100+ times and keep loving it more. It’s commonly known as Muffat’s Passacaglia; there’s debate about the difference between passacaglias and chaconnes.
Debates aside, this is one of the countless hidden pearls of the Baroque, an era too often represented by stuff like The Water Music and The Brandenburg Concertos, which, great as those pieces are, convince casual listeners that an entire 150-year period of Western music boils down to a handful of overused tunes. This would be like judging rock music based on a few Top 40 hits. It doesn’t help, by the way, that the only decent Youtube clip I can find of this particular piece features a frilly tart dancing in the woods for a pack of rustic ne’er-do-wells. Actually, maybe that does help.
My favorite version of Muffat’s Passacaglia is by London Baroque and Charles Medlam, available here, though only as an album-only selection. (Why oh why can’t iTunes just charge $2 for longer tracks instead of doing this album-only nonsense? Though in this case, the whole album’s well worth the $5.99 price tag.)
So play this, and pretend you’re one of the lucky ne’er-do-wells (or better yet, the tart), and give it a chance. You’ll find it sneaking into your ear a few days later.