The originals were slapstick comedies, they weren't meant to be "good", but rather something similar to Bad Pun Dog. Jokes being so silly that you laugh at how silly it is.
I haven't watched the new Ghostbusters, but I hear people reporting that the movie was just boring. It wasn't even proper slapstick.
The key to great slapstick comedy is charisma and that childishness with a twinkle in the eye. The intention is not to appeal to adults by trying to make it look serious, but rather appeal to the kid in all of us, by throwing all political correctness out the window.
If you do that, even unfunny things can be funny.
