ORIGINAL: Pelton
Katza mistake was stopping his offensive on turn 58. He like me vs Kamil thought it was possible to dig in and hold doing a back hand blow now and then.
I think this is an interesting question. In retrospect, I don't think digging in is a winning strategy for the Germans by late 1942, but I'm not sure whether continuing the offensive would be either, as I had some powerful reserves in some portions of the front and could have spanked him if I caught him out in the open.
I think the best strategy for the Germans, and one which Ketza has generally been following, is to generally go on the defense by the second half of 1942 and conduct frequent smallish offensives intended to pocket an army or two in a single turn rather than taking Stalingrad, etc. As long as he can conduct adequate recon to ensure that these attacks occur where I do not have powerful reserves, I don't think there is much I could do to stop it. Even this strategy would become difficult to implement by mid-1943, as if I wanted to I could have decent reserves all along the front. But by forcing me to keep these reserves it would significantly slow down my offensive.
Just my two cents...