Character cards are chosen in secret by players at the beginning of each round. A round is over when all of the players (who get one) have taken their turn. Regardless of the amount of players, during a turn players must first: take 2 coins or draw 2 district cards, keeping one and discarding the other, second: Either play a district card or end the turn. Players may use their character's special ability at any time during their turn. Characters are always played in the same order (ascending numerical rank) which dictates the order of the turns of players. Character choice order starts with whomever was "King" in the previous round or in the first round the oldest player. No player knows which character the other players have chosen until that Character's turn is called.
I played with 3 players, myself included. There is an additional subset of rules for playing with only two or three players which is that every player gets multiple Characters (3 for 2 players; 2 for 3 players) and therefore multiple turns per round. The theme is that of citizens trying to create the most valuable city. That be said the visual aesthetic of the Character cards is sinister and foreboding, as if the Character cards themselves are wishing ill will on the players.
After having read all the rules of the game the option to have multiple Characters and by association turns and powers was much more appealing than having only one of each of those things. It seemed to me that more fun could be had in the combing of different Characters's powers. I also liked the fact that you are supposed to use the District cards and coins received from each character to construct one City as opposed to a City per character. I also thought that playing with this many players would increase the speed of the game. After having played, I have to say none of these expectations were met. In fact I now have made a complete 180 and hold all of these expectations and new ones for a game with 4 or more players.
My expectations have changed because finding the best combination of Character cards was different every round because another player might choose one or both of the cards you need/wanted therefore destroying your predetermined strategy. On the other side of that even if you were able to choose both Characters you wanted, another players combination of Characters could have still been better than yours rendering your strategy for that round moot.
Also choosing or attempting to choose the best 2nd card took up a lot more gameplay time than I had anticipated. Trying to determine which Character would best complement the first Character often lead to choosing characters that could protect the first chosen character from negative effects.
There were also a lot more unevenly matched rounds than i thought there would be I.E. players either dominating the round or getting rocked. However, the replay value is through the roof. Gameplay with less than three players or more than three players is changed dramatically because you then have three Character cards or one Character card respectively, per round. Furthermore the game came with extra Character and District cards that can be swapped out with some of the original cards in order to breathe new life into the game if the players feel it becoming stale.
I don't believe I have enough authority on Citadels to say "yes it's fun" or "no it's not fun", but I can say I was very excited about the prospect using multiple Characters (3 players) and was disappointed at the outcome. However, I liked the fact that it was so different than any other game I have ever played because of which, I still had a good time playing. Now I'm excited to play it again with more people (4-7) and experience how much the strategy, player interactions, and progression of the game are different.