without going into all the rules, what makes this game fun is that it lets everyone have what i perceive is a more equal fun ratio than other games where it's very clear who is going to win at some point into the game. in settlers, nothing is inevitable and nothing is set in stone. instead of one conventional path to winning, there are different methods of procuring the points needed for victory, and it's also fairly easy to be sneaky about your progress in the game. there's also a much more human element of trading, which i immensely enjoy. in the past month, "sheep for a brick?" has quickly become a common phrase of my lexicon!
i've played with a bunch of different groups, people, ages, and levels of experience, and the consensus has always been that settlers of catan is an extremely well-crafted game that draws you in the more and more you play. if you ever get the chance to play it, definitely give it a shot - the learning curve is totally worth it. and if you want to own the precious, i recommend buying it on amazon, as that's the least expensive option i've seen thus far. happy settling!