While the bomber doesn't make an appearance in singleplayer, the B-2 makes an appearance in multiplayer as the Stealth Bomberkillstreak for all sides, a 9 killstreak which carpet bombs a large portion of the map. During the bombing, the plane doesn't appear on enemy radar, but is very loud.
The B-2 is the loudest of all the planes in Modern Warfare 2 and can be heard even before it enters the map.
B-2s cannot be shot down at any point in-game. However, an EMP can stop it from dropping bombs mid-run in Modern Warfare 2. This changes in Modern Warfare 3 where the B-2 will be destroyed when an enemy EMP is detonated.
When watching a killcam with a B-2, the player will notice that the top of the plane is very low detailed. The cockpit and other physical parts are just textures, and that the top of the aircraft is mostly smooth, and slightly angled.