Communication between the Game Master and the players is crucial to keeping the game fun. Solicit feedback from your players from time to time and see how they feel about the experience. If they curse, spit, or stab you with a pencil, it means they probably aren’t happy with the direction the game is going. Sadly, there isn’t much you can do about this, unless you want to give them their way. And honestly, what’s the fun in being the GM if you’re just going to let players have their way?
UPDATE: Ah. So THAT’S where the “rocks fall” joke originated!