Standards - please let teachers know exactly how each game meets specific standards - while all of the previously mentioned items are important it is standards that are important at the end of the day.
Thus, if we can show that a game makes it easier and fun to learn a concept or meets a specific standard or part of a standard and is fun, easy to use in the classroom, and improves the overall learning experience and retention we have a winner.
I would use the national standards available at http://www.education-world.com/standards/national/index.shtml as these are put forward by educators at a national level and try to cmply with state standards across the board.
By showing what standards a specific games content meets it becomes a viable educational resource for the classroom instead of a feel good thing to add to existing materials. Moving it from dessert to the main course.
Pat Fuge
Gnome Games
www.gnoemgames.com