I think Germany very likely could have won the war if Hitler waited to attack Russia until after Britain had been knocked out. Germany then could have focused on Russia without having to split its forces. If they'd done this and if Hitler hadn't decided to deviate from the established plan, German forces likely would have rolled over Russian forces before they'd had time to dismantle and move their industrial capabilities to the isolated East. This would have prevented Russia from being able to build up the necessary tanks and material resources needed to beat the German Army. Zukov was not a great Commander, but he was competent and after Russia was able to build up the forces necessary (usually more than twice what the Germans had in any given battle) he was able to win on sheer numbers alone (tho the T-34 was an amazing tank).
Again, it always comes back to Hitler making stupid decisions that had disastrous consequences down the road.
It's almost impossible to overstate how disastrously incompetent the Nazi state was. Germany started the war as the most powerful country in Europe, and ended the war as the 6th most powerful country in Berlin. The German Field Marshalls that got to write their memoirs after the war like to absolve themselves of blame by pinning all of the bad decisions on Hitler himself. The reality is that Hitler made just as many good decisions as he did poor ones.
Operation Sealion could be a whole entire case study of how poorly thought out German war plans were. The Germans were not at all experienced in amphibious assault and planned on using motorized river barges to cross the English channel and capture a deep water port in tact to offload the rest of their Army. The barges would have likely floundered in the Channel on any but the best of days. Many of them would have sunk even if the Royal Navy didn't shoot them. They would have had no naval fire support. No air supremacy. Their airborne troops would have been made into mincemeat like they were in Crete, but on a larger and more disastrous scale. The Kreigsmarine surface fleet would not have mounted a serious challenge to the Royal Navy on even the best of days. Germany lost 50% of its Destroyers, 50% of its heavy cruisers, and 30% of its light cruisers in the Invasion of Norway. The Kreigsmarine surface fleet could never go toe-to-toe with the British home fleet.
The Wehrmacht would not have been better off to attack Russia at a later date either. It is not like the Russians were asleep at the wheel and not already making their own preparations for war in 1939. The relocation of Soviet industry to the East was already taking place prior to Operation Barbarossa. The Red Army was also in the midst of modernization and reform in 1940, and weakened from the Winter War against the Finnish, that Hitler saw it as his best chance to conquer Russia, and he was probably right. The success of Barbarossa was mostly because of its timing; not because of inherent superiority of the Wehrmacht.
That brings me to the next point. Enemy at the Gates is not a documentary, and the Russians didn't defeat the Germans because of manpower alone. Once again it's an area of history that was widely colored by Nazi Field Marshalls writing their memoirs after the war, and their accounts were in large part biased from their beliefs and desire to save face. By the middle of the war, the Soviets had tactical parity with the Wehrmacht, and only by including civilians that the Germans purposely starved, bombed, or killed, do we get to the ridiculous idea that the Germans inflicted 10:1 or 20:1 losses on the Soviet Union. They blamed Hitler, or their unreliable allies, or human waves...basically everyone but themselves. The reality is that the Wehrmacht was not just bested by "unfair" strategic advantages, but they were also bested at a tactical level.
Moving on from that, even without the Soviet Union, the Germans would have lost. The Germans were horrible strategic planners, and their inability to produce the same amount of war material as the allies wasn't due to lack of resources and raw material...but also because German industry was incredibly inefficient on it's own. A German factory was in no ways equal to an American one. America produced as many M4 Sherman tanks during the war as Germany produced tanks of all types from 1939 onward; that's including Panzer I's and IIs. And American tanks were qualitatively better, even compared to the later German tanks, which had a bad habit of breaking down, setting themselves on fire, and having file-to-fit parts.
As a state, Nazism was incredibly bad. The V2 program, their tanks, jets, and everything else that gets held up as examples of Nazi technological superiority falls completely apart on examination. The Allies didn't concentrate on producing heavy tanks, rockets, or jet fighters because they couldn't, but because they appropriately weighed their value, and decided against it. The Germans pressed their jet fighter into service before it was ready out of necessity; not because they were qualitatively ahead of the Allies. It's a pretty common trend that German wonder-weapons have some sort of fatal flaw that their fans won't tell you about, or deliberately understate. The Panther tank was a heavy tank powered by the motor from a medium tank that had a bad habit of setting itself on fire, and blowing up its transmission. German jet engines didn't have nearly enough longevity to be practical on a wide-scale. Their efforts at a strategic bomber are equally laughable.
"The cost of the development and manufacture of the V-2 was staggering, estimated by a post-war US study as about $2 billion, or about the same amount as was spent on the Allied atomic bomb program. Yet the entire seven-month V-2 missile campaign delivered less high explosive on all the targeted cities than a single large RAF raid on Germany. While such a massive expenditure might have been justified if it had had a military impact, the V-2 accomplished nothing of significant military value." - V-2 Ballistic Missile 1942-52, Osprey Publishing.
That gets us all the way to the Manhattan Project and superior
Jüdische Physik. If Germany somehow manages to hold on longer than it did, Berlin and Hamburg get nuked in 1945 and surrenders.