|Yes, maybe a little beverage helps....|
Chemistry is inexplicable to those outside the game. In many ways, it's like obscenity- "you know it when you see it". I've had some games that were hilariously fun and I couldn't wait to play- but people watching from the outside had no idea what was good about it. I've also had games that, on paper, were stellar. Well known GMs, great players, interesting plot- but when the group was together, the chemistry was terrible and the game fell apart.
Recently I've seen games with great starting chemistry lose steam because a member of the group had to quit, and I've seen dying games take on new life with the addition of a single player. I've been impressed by the fact that in most cases, the key to good chemistry is a SINGLE person with a dynamic personality. At least in my area, when you add more than one 'big voice', things kind of go off the rails.
There's no crystal ball as to whether a game will work with the people in it or if you need to do some quick chemical adjustment. Because chemistry is fairly important to me, I often sit in on a session or hang out with the group I am considering joining before I agree to play in a new game. I know other people do a sort of interview to figure out if the people they will be playing with 'fit their needs' and others just hope for the best.
What experiences have you had with group chemistry, and what advice do you have for those having problems?