TL;DR Skip to the end for a conclusion, sorry for the wall of text.

I'm going to answer my own question after briefly doing some reading:

Although I haven't read a great deal of literature on the subject, this piece by Clive Pearson is an excellent source that answers this question to virtual perfection.

Here's a condensed version of the article, in both my own words and Pearson's.

After explaining the state of the Soviet economy and armed forces in the interwar years, Pearson goes on to explain the three phases of Stalin's leadership during the war: disaster, Soviet counter-attack, and Soviet victory.

The first phase involved a slow reaction to the German invasion of the Soviet Union by Stalin, and subsequent failures as the German army advanced quickly, using its doctrine of Blitzkrieg. Nazi forces besieged Leningrad by September 1941, just two months after the invasion. A string of failures resulted in the German army knocking at Moscow's door, where Stalin had decided to remain.

The second phase: Stalin realised he could not retain full control and win the war, and so allowed his best commander, Zhukov, more flexibility. New armies would be built up, well trained, and kept in reserve until the time was right for a counter strike. Pincer movements by Zhukov turned the tide, and forced German commander von Paulus to surrender in January 1943. After an expected German attack at Kursk in July 1943, the Soviets successfully defended and forced a Nazi withdrawal.

The third phase: From July 1943 to the end of the war, Stalin matured into what Zhukov called something approaching 'a real military commander'. After the Kursk counterattack, further attacks were made, such as Operation Bagration, resulting with the liberation of Kiev in Ukraine. Knowing that an end to the war was in sight, Stalin made the capture of Berlin into a race between commanders Zhukov and Konev. the campaign was rushed and resulted in major casualties, though this was never a concern for Stalin.

Stalin also contributed greatly to the Soviet victory for a number of reasons. He organised the transportation of factories, machines, and 25m workers and families to beyond the Urals, where the Soviet economy could outproduce the Germans in artillery, tanks, and aircraft by two or even three to one. Stalin mobilised the whole population into the war effort. He exploited Allied aid, notably the Lend-Lease program from the US and UK. He was a clever diplomat and played Churchill and Roosevelt off each other, conceding very little but gaining a lot.

So in conclusion, Stalin was crucial in winning the war for the USSR because of his decisive roles in military and economic strategy, and turned near collapse into triumph. Despite the victory, Stalin's legacy is far from heroic, as his conduct in the first 14 months of the war nearly resulted in catastrophic defeat. While Stalin could enjoy his victory, 27 million Soviet war dead could not.