By fun in this article I mean is engaging, fast paced and chaotic. Elements which are usually traits of a Party Game but whether your game is a party game or not you may find these tips helpful for you board game anyways. Here is a list of the things you should be considering when designing a co-op board game for choatic fun.
1. IS IT MY TURN YET....
It is NOT FUN to wait for someone else to make a decision or wait for someone else to role dice. Consider carefully how long player turns will take. In fact you can remove player turns altogether and create a democratic system for making decisions. If you have a coop game do not just make a single player game that you play with friends make it a TEAM experience.
2. FIGHT TOGETHER, FIGHT EACH OTHER?!
Members of the group should feel essential to the group but also they should not feel that they always need to follow the group. Conflict between group members create unpredictable outcomes which creates chaos and fun even if it means that sometimes a group member does not get what they want.
3. THERE IS NOT ENOUGH TIME?!
Consider adding a timer to an aspect of the game. This adds a totally different dynamic and creates agency to the player experience. If you want to create instant chaos combine a difficult and dividing decision that needs to be made as a group and add a short timer that forces the group to make a decision quickly. If an experience is not engaging players the way you want them to be engaged a timer might wake them up.
4. Randomness but not too much...
Either use dice or cards to create randomness. Combining both is usually to much. Try to create Controlled Chaos! The player should feel that their choices matter but sometimes the outcome does not work out the way they wanted it to.