There is something about the "build something and then see how well it does" genre of games that I really like. Cargo Bridge falls right into this category (Fantastic Contraption is another game of this type that I like). The point of Cargo Bridge is to make a bridge that spans a gap or two that is constructed well enough to hold the workers and the cargo. The trick comes in that you only have a limited about of money to buy supplies with so some planning has to be used. The game starts with just wooden pieces that are light and cheap. After a couple of levels there is also an option to use metal pieces which are more rigid, and can have longer spans, but are heavier and cost more. The challenges given always seem fairly easy but they have twists thrown in, so different building style has to be used. This game is getting heavy playing time on my computer, you might want to give it a shot as well.
Oh, also the workers give off a satisfying yell as they fall to their death, so even when I don't make a good bridge I still get some entertainment from it.