GTA: Elona Shooter
The castle is very prosperous because it have a wonderful king that manage it. However, there are bad guys, who want the castle and all of its riches. The king would not let that happen, so they hired you to defend the castle. Defend the castle at all cost. If an enemy gets too close then they will destroy the castle and that is something you want to prevent. Some enemy drop money, which you can use to buy upgrade, repairs and for a lot of things after every level. It is a great idea to focus on your economy first before anything else.