I like this model ! If like me you're a beginner in Blender, you will be surprised that it doesn't animate at first when you press alt+A. I found out there were two steps for that :

- in the dopesheet editor, go to Action Editor and select (for instance) the Walk action.

- in the NLA editor, the Walk line is now green, click on the "pin" button on the Walk line, toward the left. Not sure what it does exactly, but if you press Alt+A you'll now see the walking animation :)

My engine doesn't even support IK yet, but I will try to use this model in my next game, thanks Quandtum :)