Well they didn't get a whole lot of opportunity to show their skill (or lack thereof, whatever the case may be). When the Germans attacked, Dutch defenses were overrun in 4 days. At the end of the war, after Normandy, Dutch forces fought under allied command.
The Netherlands had a policy of armed neutrality. The period from the mobilisation in the summer of 1939 to the German attack in May 1940 shows that the Dutch high command was divided in how to meet any German aggression.
This map will be useful in the following discussion.
All generals agreed that a defense at the border was hopeless. The border was too long and there were few defensible positions. Even a defensive line along the Maas and the IJssel, the easternmost rivers, would be too long. Some units were stationed there, but their purpose was not to stop the enemy advance, but to delay it - for instance by blowing bridges and occupying key positions.
Supreme commander general Reijnders wanted to put all his cards on the Nieuwe Hollandse Waterlinie (New Hollandic Waterline), defending only the main Dutch cities in the provinces of North and South Holland and Utrecht. Dutch forces would then hold "Fortress Holland" until French and British forces could join them and drive the Germans out of the rest of the country.
Reijnders wanted all military action in the rest if the provinces to do nothing more than delay the enemy advance. He considered the field army to be incapable to do more due to lack of training and equipment. The Grebbeline and Peel-Raamstelling would be manned, but withdrawn at first contact.
The commander of the field army, general Van Voorst tot Voorst, was insulted by this lack of confidence in his army and ignored much of the instructions. He thought the Waterline was too static and instead decided to make the Grebbeline the main line of defense. From there the army could make manoeuvres into the east of the country. Furthermore, the units and the Peel-Raamline would not withdraw all the way to Holland, but instead take up a defensive position along the (shorter) 's Hertogenbosch-Tilburg line (not shown on the map since it was not used, as we shall see in a moment).
This disagreement and a political issue (Reijnders had problems with socialist 'military reserve' initiatives) led to general Reijnders being replaced by general Winkelman. This happened in February 1940. Winkelman considered the Waterline to be too close to the population centers, so he made the Grebbeline the formal main defensive position. He did however insist that the units from the Peel-Raamstelling would withdraw all the way to Holland - acting on secret information that the French and Belgian forces would not be able to link up at Tilburg in time. In light of the German attacks on Denmark and Norway, Winkelman also paid extra attention to the defenses of airstrips in Fortress Holland.
On May 10th, 1940 the Germans attacked along a broad front and landed airborne forces at bridges at Moerdijk, Dordrecht and Rotterdam as well as at airstrips inside Fortress Holland. The landings at bridges were largely succesfull, creating a gap in the Waterline. The main thrust of the Germans was through the province of North Brabant ('defended' by the Peel-Raamline) to Moerdijk. By the end of May 12th the Dutch position had become untenable. On May 13th both the Waterline (at Moerdijk) and the Grebbeline had been broken. The German carpet-bombing of the city center of Rotterdam on the 14th was used by the Dutch high command as an excuse to surrender. Fighting wouldn't have lasted much longer in any case.
So, how skilled were the Dutch generals during World War II? As has been discussed above, the Dutch were in an impossible position. Their army was not very well trained, didn't have proper equipment (the Dutch army had exactly one (1) tank. Not one tank division or one tank brigade - one tank...). The Dutch generals disagreed on which impossible plans would be best to hold this impossible position. Something can be said for - and against - each of these plans. All generals correctly understood that defending more than Holland/Utrecht was utterly hopeless, they just had to think of something to keep that last bit of the Netherlands in Dutch hands long enough for help to arrive. In hindsight, no option would be able to do that.
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