The fantastic Board with Life blog posted an interesting idea last month, suggesting a new set of metrics for assessing the size tabletop games. They are identified as:
These are collectively used to measure the size of a game. Rather than replicate the post here, I will link to the original article:
Catan Blues: Three Dimensions of Tabletop Gaming – http://wp.me/p7wmK4-CH
It makes for a very interesting read!