Was the 1940 Fall of France 1 of the biggest military upsets ever?

[America Needs a 13-6 Progressive SCOTUS]

Absolutely, the incompetence and complacency on the part of the French was staggering.

[lfromnj]

Relatively shocking but It happened in 1870, near happened in 1914 as well .
Germany's Ruhr valley had some key population distribution advantages.
Still quite incompetent but not that shocking when looking at it. One thing to note is that Germany didn't have too many significant material advantages.  
Their tank quality overall was probably maybe a little bit better than the French and the French had the much superior Somua
S35. It was the specific advantage of using mass tank attacks that gave Germans a sorth of defense in depth.

[H. Ross Peron]

Relaticely shocking but It happened in 1870, near happened in 1914 as well .
Germany's Ruhr valley had some key population distribution advantages.
Still quite incompetent but not that shocking when looking at it. One thing to note is that Germany didn't have too many significant material advantages. 
Their tank quality overall was probably maybe a little bit better than the French and the French had the much superior Somua
S35. It was the specific advantage of using mass tank attacks that gave Germans a sorth of defense in depth.

The difference was that in 1870 and even somewhat in 1914 (given the small size of the BEF), the French Army was largely alone and not supported by the British Expeditionary Force.

[lfromnj]

Relaticely shocking but It happened in 1870, near happened in 1914 as well .
Germany's Ruhr valley had some key population distribution advantages.
Still quite incompetent but not that shocking when looking at it. One thing to note is that Germany didn't have too many significant material advantages. 
Their tank quality overall was probably maybe a little bit better than the French and the French had the much superior Somua
S35. It was the specific advantage of using mass tank attacks that gave Germans a sorth of defense in depth.

The difference was that in 1870 and even somewhat in 1914 (given the small size of the BEF), the French Army was largely alone and not supported by the British Expeditionary Force.

I mean the BEF wasn't even that large in 1940. It was like 15% of total forces

[Pink Panther]

I would have to say yes. Although it already happened in 1870 and nearly in 1914, as stated before, I don't think anyone saw that happening again. It was believed, due to the supposed weakness of the German Army and the wide expectations of the Germans attacking through the Benelux, the French would be able to repel the Germans at first, though in hindsight, there were massive warning signs, especially in the Poland Campaign.

[Statilius the Epicurean]

Yeah, Fall Gelb was a massive gamble that shouldn't have come off. It's a good example of the importance of contingency in history, and in war in particular.