I just watched GB2 again. I noticed this before but it really stood out to me this time - Peter and Dana have a real relationship which is almost completely separate from anything happening in terms of plot. In the first film he is hitting on her constantly... even though she is way, way, out of his league. There is a new documentary about the first movie and that is discussed. Obviously by the time of the sequel they have real history. Even though Venkman is doing his usual goofy antics he clearly cares about Dana and her baby. Real chemistry between Bill and Sigourney. Where in the first she was more slightly amused and irritated with him. Actual character development. Which is an unexpected highlight in what is really a comedy.