Right, total fantasy here but why not. Suppose for whatever reason, perhaps easiest unexplained, the full might of 1940's Germany suddenly appears today. Firepower, troops tactics etc. Full attack mode. How far would they get today? Would our superior technology cut them to ribbons in the blink of an eye or would the political climate we "enjoy" today mean that while the EU was drafting a resolution condemning them they would have swept the continent?

Against a modern army, I would give them about 5 minutes. German artillery could not penetrate modern tank armour, modern tanks would annihilate any German armour, just computer assisted artillery would be enough to flatten any German advance. And if you factor in airforces it would be game over before it started.

However in a low tech infantry battle then it would be hard fought. As you saw in Vietnam, Iraq, Afghanistan etc divorce modern forces from their armour, planes and technology and it comes down in some part to training. WWII era weapons are just as effective as today. The standard German machine gun is virtually unchanged as is much American kit. I suppose modern armies would have greater firepower at their disposal but the differences would not be insurmountable for a German army.

If the entire WWII German army tried to roll into modern France now I tend to think they wouldn't last very long at all.

The German attack of 1940 consisted of an attack against Holland and Belgium designed to draw in the Brits and French, followed by a main attack through the Ardennes to cut the Allies in half.
One modern aircraft with IR cameras or synthetic aperture radar would reveal the German deployment and remove the element of surprise.
The Ardennes is naturally easy to defend, hence a few hundred light infantry with modern anti-tank missiles would hold up the main attack.