This is something I'd like to see what people think, since opinions can vary so much. Basically: What is your favourite game of all time, and what do you consider the greatest game of all time.
Rules: Don't belittle anyone for their opinions if you can help it, you don't have to give any justification for your favourite game, but a justification for your opinion of the greatest game is preferred.
My Favourite Game: Star Wars: Knights of the Old Republic II. I don't necessarily know why, but I am seriously addicted to this game whenever I play it. It's very severely broken sometimes, but I've played it through too many times to count, and always find something new.
The Greatest Game: Tetris. My reason is that it is the most accessible game that can cater to all skill levels. People who have never seen it before can pick it up really easily, but it also allows for super-high levels of play. Plus, it's a formula that has remained unchanged for a very long time but is still incredibly fun.