The debate around Zhukov's competency as a general is largely focused on whether or not his crowning achievement, Operation Uranus, was more luck than good generalship. This centres around the complete failure of Operation Mars, the offensive in the Moscow Region, that was concurrent to the offensive in the South. While the former was a great success and resulted in the battle that many would argue turned the tide for the Red Army, the later became known as 'the Meat Grinder' for the numbers of men it claimed. After the war, Zhukov, among others, would claim that Mars was a diversion for Uranus, but a lot of military historians tend to actually think the opposite; that is, that Uranus was actually meant as a diversion for Mars. This makes sense because a significant number of German tanks were operating in the South, and containing them there would prevent a shift of armoured forces north. The Germans had already demonstrated that they were able to quickly redeploy their Panzer Armies in 1941 when the need arose. Basically, the idea that some WW2 historians put forth is that Uranus was designed to hold those tanks, while Mars would be the main thrust. This makes sense given the importance of the Moscow front. It also makes sense if you compare the size of the forces. Mars received more tanks and combat aircraft than Uranus, as well as more men per mile of frontage. So, if we assume that Mars was meant to be the main thrust, and Uranus the diversion, then Zhukov looks a lot worse. By this way of thinking, the success of Uranus can mostly be attributed to luck, while Mars itself was an abject failure, nicknamed the 'Meat Grinder' by Soviet troops fighting there. Now, even in this case, Zhukov and other Soviet commanders did an excellent job in taking advantage of their good luck in the South. However, this narrative places most of the reasons for their success squarely on the shoulders of Hitler and German commanders on the ground, which of course robs Zhukov of some of his claim to fame.

Zhukov and Soviet historians actually claim the opposite though. That is, that Mars was meant as a diversion for Army Group Centre to prevent it from coming to the aid of the Army Groups in the south. And this is exactly what happened. Similar to the Battle of the Somme's impact on Verdun, these two huge offensives prevented either sector to effectively reinforce the other, and was particularly hard on the Luftwaffe. If we accept this narrative, Zhukov looks much more favourable (if a bit cavalier with his soldiers' lives).

Ultimately, one's view on this is going to depend on how one weighs the evidence. I am personally of the view that Mars was meant to be the main offensive, and to me the main evidence for this stems from the weight of equipment allocated to it, something a number of WW2 historians rely on as their rationale. It seems improbable that devoting such a huge number of men and equipment to a diversionary attack on a salient was meant to be anything but an attempted breakthrough. In many ways, it was similar to the German side's failure at Kursk, and no one would argue that battle was anything but an attempt to surround and destroy the entirety of Soviet forces in that salient.

None of this is to say that the man was a bad General. And there is much to be said for the way he helped turn around Soviet fortunes. However, I think that the debate about Mars sort of helps crystallize whether he was a great general or not.