IMHO it's a sim. Some argue that it's a game. I feel it's a SIM because there isn't scoring and it tries to model actual flight physics. There are no objectives to make kills or score points like a game. The main objective is to fly from point A to point B by applying flying principles. The aircraft can fly under visual flight rules (VFR) or instrument flight rules (IFR), just like a real plane.
If you let the average kid play this. And you told him to fly a Cessna 172, from KFXE (Fort Lauderdale Executive Airport) to MYEH (North Eleuthera Airport in the Bahamas) and told him/her at the Cessna's rate of speed it's going to take an hour plus just flying mostly over the ocean, and nobody is going to shoot you down and you can't shoot anybody either. And make sure you have enough fuel, otherwise you'll crash. I have a feeling he or she would soon be saying what kind of crappy game is this.
Atlantic ocean is what you'll see most of the "game "!
Finally as of today X-Plane’s own home page say’s “The world’s most advanced flight simulator”.