I very recently watched both.
Now, bear in mind: I still prefer the sequel over the original.
But here were the big differences I noticed, and something to consider:
1. Harold Ramis has stated in the past that the movies were “serious comedies”…meaning the plot was pretty much as important as the comedy, and it totally makes sense.
That said, the first flick had a very upbeat, light-hearted feel to it; the plot was kind of important, but the comedy seemed a bit more important, and implied where necessary. The sequel by contrast was much, much darker, and seemed to emphasize the plot over the comedy; not a massive biggie in my book, but it was definitely noticeable.
2. People complain about my man, Vigo…stating that he was lame and a pushover.
First off…how do you honestly top a Sumerian god? The plot of the first movie has them fighting a Sumerian god–Gozer– looking to destroy civilization.
What I also noticed, however, was the the damage she did seemed for the most part pretty limited to what happened on the Shandor building…and it was Walter Peck's interference that caused the bulk of the rest of it. Not all of the rest, mind you, but considerably a lot.
Vigo on the other hand managed to terrorize all of NYC by using citizens' negativity, and turning it into a river of slime that, technically, he fed off of for energy.
A lot of people have even complained that Vigo was defeated very quickly. Um…watch the first one; Gozer goes down pretty fast too; sorry, I noticed it.
Also worth noting about Vigo: baby Oscar and the crowd outside of the museum pretty much saved the Ghostbusters, and helped them defeat him. Not only did he possess Ray, but he also managed to use the energy from the proton packs on the Ghostbusters, and keep them paralyzed.
Gozer….simply terrified Egon beyond the capacity for rational thought. Well, true…she did turn Dana Barrett and Louis Tully into Terror Dogs.
My whole point is, while I now see why people prefer the original, I'm trying to explain my perspective as well.
Of course, I prefer Real Ghostbusters over both
