GTA: Steam Punk Tower Defense
The enemies are attacking, but you are confident that they aren't going to break in the defense because you have one of the most high tech fort in the world. In this game, you need to defend your fort against enemies advancing to your fort. This would not be easy since there would be lots of enemies and this is the same reason why you would need to buy more guns to defend your fort. The game would be harder if you are not going to put in more guns for defense purpose. Take note that there are several varieties of guns that you can buy.