Virtual Villagers, like all of our real-time games, is designed to be open-ended. Each game has clear goals, but the games can continue to go on and allow you to play as long as you like. The Island Events will continue to happen, which can dramatically change the way things are going for your villagers. You can also try to get a higher ranking in our online High Scores page. Once you get tired of your current game, you can do like most people do and play the game again on different settings and/or try different strategies. The puzzles aren't as stressful the second time, and you can try completing them much earlier in the game.

This thread contains links to several good discussions on that topic!