Robert Meyer Burnett lit up YouTube a while ago when he stated that, "Ghostbusters 1984 is Not a comedy".
Now, I actually agree with Robert, Ghostbusters is a mystery-thriller cake with comedy icing on top. But the real effect has gotten fans talking about why we all like Ghostbusters. Movie magic happens when you mix genra types and Ghostbusters is an excellent example of how it's the level of the mix that creates a great movie.
Ghostbusters, the 1984 movie, has been described as "lightening in a bottle", a once in a lifetime confluence of circumstances (some not planned), and because of that it's unwise to try to re-capture that magic moment.
Now take just one aspect of what this all means.
Many of Bill Murray's ad-libs were so good they were included in the final cut because good actors mesh with the flow of their character and are able to add that special touch few writers ever put in scripts.