The ultimate goal is a fully self-sufficient town that can withstand any disaster. This means having robust food production from multiple sources, a massive surplus of firewood and tools, and a diverse economy. You should be able to produce all essential goods internally, only relying on trade for luxury items or specific seeds/livestock to diversify.
Once self-sufficient, you can focus on aesthetic improvements, building monuments, or simply watching your town flourish. Experiment with different town layouts and production chains. The game has no 'win' condition, so the challenge becomes how large and efficient you can make your settlement while maintaining citizen happiness and survival.