Kingdoms and Castles is a simulator that places you in the role of a ruler who must decide how best to build up their kingdom. It offers you plenty of options for doing so, along with plenty of challenges.
Your most basic goal is keeping your people happy -- partly because that's what good rulers do, and partly so that you can tax them without fear of revolt. You're also responsible for keeping them fed and healthy, which means allocating resources to farming, to better buildings, and so on. But in return, you also attract new residents to exploit -- er, care for.
There are other challenges too, including marauding Vikings and dragons that mercilessly sack your kingdom if you aren't militarily prepared for them. The biggest pleasure, though, comes from building and managing the layout of your kingdom itself, and the layout of things like towers and walls that change based on how you stack your tiles and choose to build.
Ultimately, how and where you build your kingdom determines your success or demise. It may not have quite the depth of Civilization, but Civilization also doesn't have dragons…