Many reviews have already dug into the specifics of the game, so I won't repeat them.

This is a fun game for players of all ages. Adults will play with much more strategy, of course. There are different options for strategy: go for longest road, go for biggest army, go for development cards, go for cities, etc. You also have to think about what resources you want to build next to, knowing that which resources you need will change throughout the game.

This is most fun with 4 players, as it makes it the most challenging. Of course, it then can become easy to be cut off from parts of the map, or unable to expand. Technically you can play this game with 2 people, but it's a bit too easy and thus not very exciting. There is a 5-6 player expansion, which makes the board larger.

There are of course many expansions to this game. Seafarers is a blast and is an easy transition, as it makes only minor changes to the game, but really changes the strategies you can use.

Highly recommend this game, especially for people who are not big into board games. (This is often considered the #1 "gateway" game.)