There are many first person shooter games on pc and smart phones. But if you have played counter strike source, you must know how amazing that game is. Best thing is this game never ends. You can also play online with your friends or other players. If you get of bored of old maps you can also download new maps in it easily. On smart phones this game is fun but not that much as compared to pc, but it is very fun game on smart phones also. It can be downloaded on android and ios also.