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@Wendell: I think I might make two maps when the war ITTL is over: One for the advancing and retreating of the Germans, and one for post-war Europe.

Not really a retcon, only something I forgot:
During the time before Barbarossa (June '41 - May '42) the Germans use the opportunity to destroy the resistance throughout Europe. Yugoslavia and Greece are pacified, and the French resistance also suffers greatly. Among the killed partisans also is a Croatian Communist named Josip "Tito" Broz.

After the Western Allies have taken Sardinia and Corsica, FDR and Churchill decide to strike against the Balcan. Stalin isn't that happy about that (he had hopes in the past that he could make gains there after the war), but he isn't really in a position to demand it, since the Germans occupy more of Russian territory (and the Soviet Union is weakened more than OTL).
In October, Allied troops are brought from Apulia in Southern Italy to Albania (which was occupied by the Germans after Italy gave up). The mountainous land makes an advance difficult, but the local population helps the Allies against the Germans. During the winter, Albania, Greece and southern Yugoslavia are liberated. Now Bulgaria fears the worst, and after the Allies reach their border, the government makes an armistice and declares war on the Axis shortly after.

The Balcan offensive was necessary for the Allies, especially Churchill, because in '44 the Germans started to send V-rockets (the so-called Wunderwaffen) against London and other places in Britain. The damage is not that high, but no trifle either. And since a landing in France isn't possible now and the Germans manage to hold in Italy along the Apennin, the Allies need a victory.

After Bulgaria switched sides, the Germans destroyed most bridges over the Danube, so Romania is still secure; only the Dobrudsha is conquered. Stopped before Belgrad, the Allies move their Balcan offensive west, into Bosnia, which is part of fascist Croatia under Ante Pavelic. The oppressed Serbs join the Allies in masses. Dalmatia is conquered too during that time.

In January, president Roosevelt died (for him, especially the time when Hitler conquered half of Europe and he couldn't act against him was harder than OTL). Hitler is glad and believes that the tides of war may turn, just like 1762 for Frederick the Great. In one way, that's true: New president Harry S Truman is more anti-Communist than FDR. Of course, the US stay in the war.

After they liberated Leningrad and repaired the rails leading there, the Soviets start a new offensive against Finland. The Fins see that they've lost and capitulate in February '45. In Norway, the Germans continue to hold out under general Dietl. At the same time, the Soviets have also advanced in the Northern Russia, where they drove the Germans back to the Baltic states, and in the South, where they took the Crimea.

In the spring, GIs land on Shikoku. The following fight is very hard; the Japanese are almost lost, but fight the invaders to the last man, don't surrender at all, and make kamikaze attacks on US ships. Truman decides that it might be a better idea to help the Chinese, supports them with tanks. Now the Japanese are driven back in China.
(Sorry if this part sounds more boring than the European theater, I don't know that much about Asia.)

In April, the Allied attack on Zagreb is successful, and Croatia capitulates too. The Germans occupy Slavonia to continue the hopeless fight. But now, the Allies have reached the border of the "Greater German Reich".

May '45 is relatively quiet. In the East, mud prevents the Soviets from attacks, and everywhere else, the Germans hold out against the Western Allies. But the Allies have other plans...