The press screening was preceded by a video message from Jason Reitman who said "If you're a Ghostbusters fan, you're about to go on the greatest Easter egg hunt of your life." Note that he didn't promise a funny comedy or an exciting story, and he was right not to do that.
By the finale, the movie just gives up half-assedly trying to do its own thing and says fuck it, let's do the finale of the original except without the giant monster.