We enjoy Assateague Island in the winter. That's largely because we like to watch and listen to the Snow Geese. We generally go between Christmas and New Years and hope for the best. How many snow geese and other birds are around depends on the weather.
I don't know all of the variables but here's some. Assateague has several ponds or pools. How much water they have in them depends on how wet summer was. If the ponds are relatively full, there can be lots of snow geese and ducks on the island. The other issue is temperature. If it is too cold, too early the bulk of them may have gone further south. If it is too warm, they may have not needed to come this far south. Basically, you go and take your chances. There's almost always some snow geese there in December, though.
Snow Geese aren't quite as noisy as the Canada Geese. They seem to converse (is that what geese do?) in more of a murmur. If you can get close enough to actually watch them, they are a lot of fun. They leave early in the morning to raid a farmer's field. They seem to start coming back not too long after lunch.