The modern one reflects some... changes - the more contemporary window style, and the number of minifigs wearing ties in the firehouse has increased. I expect it reflects an assumption of a higher tax base in legoville. In all seriousness, the custom piece count is on full display, where the 90's set is dominated by reusable generic pieces.

Those outward-sloping windows in the 90's set were the bomb though, useful in so many cool applications - (star)ship bridges, towers, and the like. :D

Yes, the 1994 Flame Fighters is an outstanding set! My main dislike of the modern version is that the fire truck does not have a ladder (that would offer a lot of playability). The water gun just looks puny.

EDIT: still, even if I have a weakness for even older fire sets, I acknowledge that the modern lego fire stations are very good toys. My son has spend countless hours playing with the 2016 version [0], which is incredibly playable, and whose fire truck is the best.

[0] https://brickset.com/sets/60110-1/Fire-Station