Just to give you one datapoint: I played forumwarz episodes 1 and 2 pretty much like an addicted fiend when they initially came out. But I am not sure if I have been to the site in between and since (if you made an episode 3 in the interim, I don't know about it). If your TOS allows it, perhaps you could notify your users when new episodes come out? I'd personally enjoy episodes with a much longer story arc--I think that would keep your users more active and for longer--but I realize that is easier said than done.

Finally, I just want to let you know that I have always been pretty impressed by the online chat functionality that you implemented for the INICIT game.