It is very much worth playing but you could probably skip it. As others have alluded to, the storytelling is very influenced by Fromsoft (Souls games, basically) and is pretty oblique. But, even without following it exactly, the gameplay itself is still great, and the music and art do an excellent job setting up a melancholy vibe. The different zones have a lot of personality.
Addendum: having now had the chance to start on Silksong, strongly recommend Hollow Knight first. That's not because of story, but because Silksong seems like it's geared to be noticeably more difficult than Hollow Knight was, both in platforming and in combat. (One of the things that I think Hollow Knight did really well was the spread of available difficulties. Beating the game isn't too hard; getting the true ending involves a few more specific difficult tests; and the DLC added boss gauntlets that let you go pretty crazy with how hard you want to make it.)
