I recently listened to a great online seminar from the EDUCAUSE Learning Initiative. Richard Van Eck's talk was entitled "An Instructional Designer Looks at Digital Game-Based
Learning." If you have access to ELI, you can listen to the seminar in their archive:
http://www.educause.edu/Archive/8996

Van Eck's 4 principles of learning in games: 1) Games employ play theory, cycles of learning,
and engagement 2) Games employ problem-based learning 3) Games embody situated cognition and learning 4) Games encourage question-asking through
cognitive disequilibrium and scaffolding

From the Chat, a free game development tool was mentioned that might be worth checking out:
Game Maker: http://www.gamemaker.nl/download.html

A commercial game engine (that does not require hard core programming skills) is Torque - $100 for a single user. http://www.garagegames.com/solutions/games/indie/

If you can recommend any other game development tools worth investigating (preferrably free) - please comment here.