BTTF is great, the second was pretty bad, and the third was decent but not great.
Godfather and godfather 2 are two of my favorite movies, but as others have said, they are not the kind of films one watches over and over.
My Wife is a big Potter fan, which means I have seen them all. The first 2 are pretty bad (IMO) due to the clumsy, unimaginative and artless direction of Chris Columbus. They started getting decent when Alfonse Cuaron directed Azkaban. By the half blood Prince, I found them relatively enjoyable. That being said, I have zero desire to read the books, even as a kid I never really read anything that might be considered YA reading. I prefer something more along the lines of LOTR and GOT, at least for fantasy.