Since you've heard the buzz if you've made your way to this site, here is a quick overview of what the game is about and why it gets such high reviews. I won't go into a full explanation of the game rules, but hopefully you'll get a good take on what makes this game special.
Settlers of Catan is a board game that involves both strategy and luck, but the bargaining and interacting with your fellow players is really what sets it apart from the crowd and makes it a lot of fun. In this way, it has aspects of play that in the US you might associate more with "party games", but wrapped up in a clever traditional board game setup. As a final perk, the layout of the game's board is randomized each time you play for a new experience every time. The result? A light and fun game with a healthy dose of strategy that has almost infinite replay value. You'll end up laughing, scheming, and smiling each time.
The goal of the game is to be the first player to earn 13 points (referred to as 'victory points'). To accumulate these points, you'll need to strategically play game pieces on the board, each of which require a bit of work to acquire. The strategy of playing the game pieces, as well as how you go about getting them is where the fun comes in.
Round by round, players earn special game cards through dice-rolling. They can either hold, spend or trade these cards with the other players at the table. Once you accumulate certain combinations of these cards, you can cash them in at the bank for your game pieces (settlements, cities, and roads), and play these newly purchased pieces on the board. Because of the layout of the board, each player will probably be collecting different sets of cards at different times, so players will be bargaining with each other for different cards, sometimes happily trading with each other, other times furiously trying to outwit each other when a particular type of card becomes universally desirable.
What appeals to most people about the game is that it strikes a great balance of luck, interaction, and strategy. The luck factor and constant bargaining guarantee the game will be fun and quirky keeping your friends laughing and joking all night long. The clever strategy of the piece placement on the other hand, keeps the game from being a cutesy-fun-one-time party game, as you try to out think your opponents and win with your master plan. Win or lose, Settlers of Catan is always fun. It's friends-and-family strategy that's not antagonistic or too cut throat, and fun and interactive without being silly.
Have fun!