Uno is one of those card games that everyone knows how to play - a bit like snap. And if they don't, they can learn in about twenty seconds, because its rules aren't much more difficult.
It's often the case that the simplest games are the best though, and that's certainly true of uno. It might be a more a game of luck than judgement, but there's a bit of strategy involved, mainly in making sure your opponents don't manage to get rid of all their cards before you do. And, if they do, making sure they score as few points from the win as possible.