That doesn't make a lot of a difference, there will always be enough differences between two versions to make the effort worthwhile. 1916s Romeo and Juliet quite different from 1996's Baz Lhurman Romeo+Juliet.

1996

But how many films are essentially just Hamlet or The Taming of the Shrew?

Every remake is a piece of its own, even if they're based on the same story.