I wouldn't be surprised if the Ghostbusters 3 script wasn't too good. Dan Ackroyd seems to have a history of being a little too overzealous when it comes to script-writing. He once told a story about writing a HUGE treatment for the first Blues Brothers film. And of course, most know about the lengthy monologues(?) he wrote for “Ghostbusters”.
The reason why the first Blues Brothers film and the Ghostbusters films worked well with Ackroyd-penned scripts was the talented cast and crew, fine direction and strong concepts and flawless translation of those concepts to the screen.