I think the main reason that Ghostbusters 2 isn't as good, to me, is that Randy Edelman's score is severely lacking when put up next to Elmer Bernstein's work. To me, Elmer's music was like another character in GB1. It's that important. Randy's score was his typical unison monotone score. I'm just not a fan of his, generally speaking.
Not to say that Randy's score is all bad. It has its moments. But, generally, I find it to be boring and not striking the proper tone, whereas Elmer's score is so dynamic and perfectly tailored to each scene and the overall feel of the movie.
That being said, I hope that they use Elmer's original score for the new film, and have another composer who is at his level fill in the holes with music inspired by the GB1 score.
What say you?