I LOVE the first movie (my all-time favorite, besides RoboCop and Airplane) and was watching some of the second one on Bravo last night, and I think I finally realized what was wrong with it.
It's Bill Murray.
In the first movie, he's vibrant, a smart ass, and he's basically the spokesperson for the Ghostbusters. In part two, he's just an asshole, he's not even IN the uniform or has a proton pack on for the most part, and he looks bored in every scene he's in. The Dana scenes seem thrown in there just to give Murray more screen time than the rest of the busters.
I thought I remembered reading that Bill Murray was reluctant to doing a sequel, and it's definitely obvious from his performance in this movie that he didn't want to do it.
Yeah, that's the vibe I always got.
The movie is also too "light" and goofy. It's fairly obvious they tried to "kidify" it because of the cartoon series but they forgot that the reason why kids were into it was probably BECAUSE of the more serious tone/nature of it even the cartoon was fairly "dark" its first few years.
And the Ghostbuster's rap. Ugh. Don't get me started on that.
And, seriously, why is the Ghost in the logo doing the "2"?!?!? UGH. I hated that when I was 10 and I first saw this movie.
... Christ. Am I and this movie THAT old?!
I dunno, with Murray and the tone GB2 just misses a certain "spark."
SW wet and clutching a towel is nice for the couple minutes we get it...

But overall I think the movie second movie just really misses the mark, big time.
As I said, what IF Oscar had really been the product of Vinz and Zull?
What if the movie DID take a darker tone, closer to the original, and was maybe Gozer's second try at returning or another phase of her/his plan to return?
What if the Ghostbusters didn't have to friggin get back in business, and the courtroom "mundane" bust pales greatly to the Sedgwick hotel scene.
GB2 is just flawed in many ways, it makes me sad thinking of what could've been.

It's pretty telling when any number of episodes of the friggin cartoon series (pulling from memory here) are better than a motion picture.