Last time we had a family reunion, my cousin brought Settlers of Catan and we stayed up late playing it. It wasn't too hard to learn, but it really helped having one person truly familiar with the game to teach us along the way. It would have been much harder if we were all trying to learn at the same time. The funny thing was, the next morning we realized that every single one of us had dreamed about the game in some way.
It's a pretty damn good game.