Objective in Power Grid is to supply cities with power when someone's network gains a predetermined size. Players mark pre-existing routes between cities connection, and bid against each other to purchase the power plants that they use to power their cities. However, as plants are purchased, newer, more efficient plants become available, so by merely purchasing, you're potentially allowing others access to superior equipment. Additionally, players must acquire the raw materials needed to power said plants (except for the 'renewable' windfarm/ solar plants, which require no fuel), making it a constant struggle to upgrade your plants for maximum efficiency while still retaining enough wealth to quickly expand your network to get the cheapest routes.
Video review: YOUTUBE