in my experience (not necessarily your specific situation) game sites are generally low quality in terms of ecpm. Im not sure if its the younger age group that frequents them or not, but most game sites just seem to use ad networks to monitize the inventory.
We had one for awhile and tried like crazy to optimize with individual offers. At the end of the day when we just put up network tags it did about as well as it could with no time wasted.
Not that this is a bunch of helpful info, but its what I remember from our go round
