Had a nice mini-lecture yeterday from Josh on the ludology vs. narratology debate in Game Studies. (Filled a big gap in my knowledge, and made me realise that I need to
do some time in the library getting up-to-speed on this kind of thing.)
He emphasised the fact that casual gaming often relies on simple game mechanics, and that it's his opinion that the intrinsic narrative is more important than extrinsic narrative. This was illustrated by a game design using a clockwork robot, where the gameplay was heavily altered by the robot winding down.
After identifying that the majority of successful casual-play games are likley to be found on devices like the iPad, Josh kicked in with his second point that games need to have charm.
This charm can link in with the mechanics (e.g. springs are much nicer than invisible forces) or the desire to play (which was illustrated by examples like Lego, space hopper, Airfix, Raleigh Chopper, etc., and how nostalgia-laden parents are the main purchasers of expensive games -- what he called the James May effect).
This has given me a good starting point. I'm going to go away and cogitate a bit (and hit the 24-hour library).