Now, the Half-Blood Prince movie had far too many flaws, but the most nonsensical and unnecessary change is Dumbledore's surprise at the Horcrux memory.
In the book Dumbledore already knew about the Horcruxes and needed the memory only as confirmation to how many there were. In the movie, though, it seems as though he's shocked by the discovery after he sees the memory and yet he's already destroyed the ring. So that doesn't really make sense IMO. I mean, how come he's already destroyed the ring if he didn't know about the Horcruxes?