At the time, as far as my group was aware, there were three expansions: the five to six player extension, Seafarers and Cities and Knights. There’s quite a bit more now but that’s what we knew about. And, as time has gone on, my opinion about each one has basically reversed itself.
I used to think of the Five to Six Player extension as the most essential one to get. But I now think that adding more players just makes the game drag. There are much better games to play if you have six players.
I originally thought of Seafarers as the weakest expansion. I mean, it added ships and gold tiles. It didn’t really add anything new that I could see. Well, I was dumb because it adds versatility and variety to the game while still being true to the core system. (I have been told it was supposed to be part of the original game) A very important idea in the game (at least to my mind) is the modular board and Seafarers really explores the mechanic.
Cities and Knights. Man, Cities and Knights. That was a game changer in so many ways. Cities and Knights changed Catan so much it was like a different game. It added at least another level of the economy and infrastructure. It added a whole new form of conflict.
At least one friend of mine said that you don’t want to play any other kind of Catan after you first play Cities and Knights. Then you don’t want to play it again after the fifth play :D Cities and Knights added complexity but it felt like it didn’t add depth, at least compared to the complexity it added. I will say this for Cities and Knights, it did a good job of adding theme.
It didn’t take my group long to decide that we just liked four-player vanilla Catan. And, while we live now in different parts of the country, I can safely say that we all still really like Catan. It was a binding experience and the expansions were a part of that.