McNair made a very positive contribution to the conversion of the peacetime US Army to one capable of fighting a world war. He also helped trim some of the fat from units and reduced the types of divisions, which was good, given the shipping distance from the US to the battlefield. He was a very good organiser and bureaucrat.
However he showed a lack of imagination in not seeing the ongoing evolution of tactics and more powerful equipment - the tactical arms race. He showed a stubbornness that was appropriate for getting the US Army up to speed and in place in '41-'43 but was a disadvantage when things did not go according to early war US doctrine, when flexibility was needed. That inflexibility got a lot of soldiers, especially tankers, unnecessarily killed. That is why I have a harsh attitude to him. He had his time, when he did very good things, but by '44 that time was gone and others paid in blood.
I nearly forgot my manners, thank you very much for the rep!