I've been playing a lot of two player games, including getting my wife to play the night before, so it was nice when we had four adults to play. I was playing with my two brother-in-laws and one of my sister-in-laws.
My brother-in-laws have played before, infact these are they guys I learned how to play with. My sister-in-law is very new to any type of these games but she picked it up suprisingly quick. One of my brother-in-laws picked every single river tile, so we started to call him "Herr Fluß."
The board was very spread out with not many completed castles. Most points up to this point where from roads or cloisters. My sister-in-law bailed just before we were to do the final scoring. We were all saying, "Come back! We're just about finished!" but she had completely lost interest in the game. It was a little frustrating, but I was glad she tried it.
The three of us played another game and there was no love lost. We played pretty agressively and I would say that the game was played overall more defensively.
The next day, one of my bro-in-laws went home the previous night, so the remaining brother-in-law and I played two more games.
The two-player games I think are the most fun since it seems to be slower paced, and you try to plan for overall victory. But it's fun when you have more people too, due to the social interaction.