I personaly like games where your fighting someone, and at the
end of the level you can upgrade your gun, spaceship, ship, person,
etc... and i think (even though i have no idea how to make a game)
it could be very possible to make games like this.
Example:
Play UPGRADE COMPLETE!, a free online game on Kongregate
In this game you need to upgrade everything in order to win!
as i said, i think it would be very possible for a game like this
to be made into a zune game