Genre
Comedy; Horror; Adventure
Comedy
Ghostbusters isn't just a comedy; it's the comedy of the 1980's. Reitman, Aykroyd, Ramis, and the great Bill Murray were at the height of their comic powers when the movie was made, and pretty much every scene has a laugh or two... or three.
Part of what makes the comedy in Ghostbusters so timeless is that it's rooted in character. There're a million good examples, like cold, scientific Egon telling Janine that he collects
EGON:Spores, mold, and fungus
the huckster scientist Peter telling the library guy,
PETER: Back off, man. I'm a scientist.
or the overly enthusiastic Ray getting excited about
RAY: biggest interdimensional crossrip since the Tunguska blast of 1909!
Horror
Okay, even little kids probably aren't going to pee in their pants while watching Ghostbusters. The ghouls, ghosts, gods, and terror dogs are all more funny than scary: pants-peeing is more likely to come from laughing too hard with a full bladder (because you're too into the movie to excuse yourself).
Still, we plunk this down in the horror genre because all the creepy creatures are totally from that world. What's cool about Ghostbusters is the way it puts genres in a blender: borrowing elements from classic horror but playing them for laughs. The best example is probably that fact that the big boss evil monster at the end comes in the form of a giant marshmallow. Come on. That's brilliant. A marshmallow.
Adventure
The mad geniuses that created Ghostbusters weren't satisfied with only throwing two genres into the their moviemaking blender. Not only is this a comedy-horror; it's a comedy-horror-adventure.
Check out our entry on the Hero's Journey for all the deets, but the movie follows all the classic patterns of the heroes going off on an epic quest to slay the big bad monster. Here, of course, instead of traveling to some exotic foreign land, they stay right at home in New York. But by the time the city fills with ghosts and a portal opens to a hellish alternate dimension, NYC is about as exotic as it gets.