Ghostbusters II has a very special place in my heart, being the first movie I ever saw in the cinema (technically second, but I don't actually remember seeing Disney's Peter Pan since I was like 2 or 3 at the time) and it came out at a time when Ghostbusters was my little seven year old self's favourite thing in the whole world. I had a bunch of the toys, I watched the cartoon all the time (including a handful I'd taped off the TV), and I had a storybook of the original movie . . . with a two page spread fo the library ghost that terrified me, yet I kept peeking at it all the same. I think I even got Ecto-1 for Christmas just a few weeks later. So for me that movie was peak Ghostbusters fanboy time.
That said, while I certainly still adore it and don't subscribe to much of the criticism often levelled at it; I think it is fair to say that it's objectively a lesser movie compared to the first and hasn't aged quite as well overall. A lot of that is down to how timeless the first movie was by design; from the cinematography, to the prop design and even wardrobe, there's very little in terms of pop culture suffusing it. I'm not saying you can't tell it's a movie made in the early 80's, but more that it doesn't scream "80's movie" in and of itself, and thus manages not to date itself (see also: Star Wars.)
The sequel on the other hand feels very very much a product of it's time. Like the movie goes out of it's way to wave at the audience and yell "hey, look how modern and current we are!", which of course makes it feel rather dated in some ways. Aside from that, the script isn't quite as tight, some of the humour doesn't quite land and while the effects are greatly improved in terms of sophistication, at times it feels like they're leaning on the spectacle a little too much, just for the hell of it and neglected and paradoxically grounded feel that leant the first movie much of it's charm. Oh and the car's "Ecto 1-A" makeover was *hideous*!