People need to remember a few things about the Sherman.
The original tank first saw action in 1942, at that time having what would be considered a pretty good mix of firepower, armour and speed for a medium tank. Up until the Italian campaign it rarely met anything that was clearly superior to it. It was easy to produce and maintain unlike the German counterparts, factors that were important to a country fighting a war on a distant continent. Its also worth pointing out that early US military teachings said that the job of engaging enemy armour lay with the Tank Destroyers, not the tanks whose role would be primarily to support infantry. The Sherman was also highly adaptable producing a vast range of sucessful and varied modifications (various uparmoured, upgunned and modernised Sherman served with the Israelis decades after the much vaunted Panzers were gracing museums and town centres).