We played a couple more games. And my son (he is 9) even created his own faction. Painted the cards and paper figures. It was overpowered in the beginning, but I helped him balancing it a bit :-D
I'm not a game designer, and I don't even play that many strategy board games. But one problem we faced sometimes is that we both went into defence after a couple of turns and whoever went out of defence had a disadvantage. Did you experience similar situations?