I think it's easy to overlook how huge it was that France fell so rapidly. I mean these two European powers had been squabbling for centuries and France was the dominant land power in Europe for a very long time. Bowled over I think is a good term for it. pretty incredible military feat that has, maybe undeservedly, shamed France ever since.
Like I talked about in my previous post, though, the victory over France is really far more complicated than it being solely a Germany accomplishment.
* The general French attitude about war was not particularly good - heavily defensive, keen to avoid prolonged conflict and casualties, etc. Also things like Gamelins' reluctance to bomb the Ruhr (or even advance in any meaningful way into Germany during the invasion of Poland because of fear of retaliation).
* French high command was very rigid in its strategic and tactical thinking, both in terms of over-reliance on the Maginot Line and its use of its own tanks
* Major French strategic blunders (i.e. poor screening of the Ardennes, overreliance on static defensive lines, strict adherence to its prewar planning even as German advances made that impractical)
* Various logisitical errors by the French (mobilizing and then sitting around and doing nothing for months on end which weakened industrial production and hurt morale, Gamelin's HQ being poorly set up for communication with both political leaders and the front lines, the long time it took orders to get to the commanders that needed them especially when specific commanders either died or were out of contact)
* The Belgian withdrawal from its alliance with the British and French prior to World War II, undermining French strategic planning
* The poor morale of the French military - from being mobilized and taken away from home without actually doing anything other than sitting on the border while Germany annihilated Poland and then prepared for its campaign in the west
France was certainly thought of as a major power during the 1930s. But in practical terms that reputation was not really deserved by the time war broke out (let alone by the time the Germans attacked in 1940). Its political leadership was inconsistent and prone to defeatism (Reynaud, at least at first, was a notable exception), it's military leadership was inflexible in both strategy and tactics (and Gamelin himself was a polarizing figure who clashed with both political and military rivals, even ignoring his poor performance in 1940), it wasted many of its military's strong points by doing things like spreading its tank strength throughout infantry units (and almost solely utilizing them as infantry support unlike the Germans) and so on.
The German victory over France - especially the speed of it - is still impressive, but it tends to be overrated by an overreliance on France's reputation coming into the war. That isn't meant to denigrate the French (who fought bravely, even after the Ardennes breakthrough effectively ended the campaign) - it's just that the victory over France didn't really represent a crushing victory over a first-rate power; it was more of a crushing victory over a demoralized, ineffectively led power that made multiple mistakes to compound the situation.