...at the beginning instead of right. I suppose up or down might also count, like Kid Icarus, but then once the screen does start scrolling horizontally, you still go to the right.
The first that occurred to me are Super Metroid (once you land on Zebes, and only briefly) and Legacy of the Wizard (again only briefly). In Castlevania 2 you can try but you won't get very far.
It suddenly bothered me that my long overdue "game project", even without any actual irreversible construction work done on it, is situated firmly in my mind with a general right to left area layout. But does going the other way make a product stand out? Surely it has been done many times but I can only think of those three examples. However, I have been imprisoned in my cruel stepmother's tower for the past twenty years. Can you think of any?
Ah I think there is a moderately recent Gradius game with a bonus mode in which you pilot a big-core ship to the left.