I'm an unapologetic Ghostbusters 2 fan, also.

It seems to me that the first film was content to be a spoof throughout, while the second one has some legitimately dramatic moments and character development in between the comedy. It has somewhat more depth because of this, I think, despite still being very silly overall.

The reason it succeeds is that it aims higher in its writing, whereas most comedy sequels tend to aim lower in tone, trying to imitate or repeat the style of what made the original work without managing to replicate the substance. It's a rare sequel that actually manages to add new substance to what was already there before. Strangely enough, this may actually be what people don't like about it . . .