I read about Minecraft on a several blogs I read regularly. When I read about it on freeplaylife, I mentioned it to Dave in the hopes that he would check it out for the kiddos. He did, and the rest is history.
It is a sandbox game where you create your world and are limited only by your own creativity. Everyone in our house loves it. Dave especially. He plays a lot utilizing online resources and his own wit to create an elaborate world. He will play jointly with Eamon and Aine as well as by himself. Talk in our house centers around creepers, spiders, elaborate world enhancements, ways to avoid danger, and new ore/tool finds. For a low price, it has provided hours of enjoyment. Just be warned, your family may become obsessed and unable to do much else.