Okay, so: Yes, Brie can smell pretty strongly of ammonia. Bloomy rind cheeses, like Brie are what we called mold ripened; this basically means that, during the cheese making process a mold culture is introduced and actually becomes the white colored rind of the cheese. In Brie’s case, the culture used to ripen Brie, while feeding on the cheese proteins, produces ammonia and the associated smell.
If the cheese is tightly wrapped in plastic and not allowed to breathe, or stored at very cold temperatures—such that the ammonia cannot escape—the ammonia build up is so great that there is a terribly strong ammonia smell and flavor.
Often times, cheeses that you buy in the supermarket will not be able to breathe like they would in a case at a cheese shop, so it is quite common to pick up a wheel of brie from a grocery store fridge and bring it home to be welcomed by a cloud of ammonia.
As with all cheeses, if the Brie is packaged in plastic shrink wrap you must repackage it as soon as you bring it home in something that better facilitates the exchange of gases like wax paper. The wax paper wrapped Brie should then be placed in a resealable plastic bag or container leaving an opening for air to get in.
Also, before serving Brie, you should leave it out for at least 30 minutes so that the ammonia can dissipate and the cheese can reach room temperature.
Is it still good?
If there isn't visible mold growth then it's probably safe to eat; however, if the taste is not to your liking, you should probably just throw it away and get a fresh wheel.