These two issues are major problems - they only occur in multiplayer games (and from what I can tell only in campaign mode games, though I havent done enough pvp matches to see if that's really the case yet). The sound bug usually hits players at the start of a match or when joining a match in progress, and can only be fixed by exiting the game and rejoining (when affected by the sound bug, the player only hears minor background noises, and cannot hear weapons fire, footsteps, other movement sounds, or objective sounds). The ghost enemies seems to happen at the same time as the sound bug for most players, though sometimes only one bug or the other is experienced. Ghost enemies bug causes all enemies to be invisible to the player.

Other than those two issues, being able to co-op with friends would be nice =/ right now steam shows a server not responding issue for any kind of direct connect or player-hosted match.