Numbers Chapter 21:5
And the people spoke against God, and against Moses: Wherefore have ye brought us up out of Egypt to die in the wilderness? for there is no bread, and there is no water; and our soul loatheth this light bread.
Even though the manna was a spiritual form of nourishment the Jews did not appreciate the manna, which brings us back to this weeks Parshah
Deuteronomy Chapter 8:3
And He afflicted thee, and suffered thee to hunger, and fed thee with manna, which thou knewest not, neither did thy fathers know; that He might make thee know that man doth not live by bread only, but by every thing that proceedeth out of the mouth of the LORD doth man live.
So Wasn't the manna a good thing?
I think it was God's intention in feeding them manna was to teach us that not everything that seems good is really good to us.
As it says which you did not know and your fathers did not know. It is normal for people to prefer things they are used to, so if they are brought to a different spiritual level they do not appreciate it, since they are not used to it. They want to remain a slave to this world.This is the nature of our ego. The same is true here, especially since the manna was a spiritual food, and physical beings desire only physical food.
In Talmud Taanit 21a it says This misfortune too, is for the good even though it appears evil to everyone.
In order to teach you that man does not leave by bread alone means everything God decrees, whether it appear good or bad; on our level of understanding in this physical world man shall live better. Therefore, do not despise God's discipline. It may be a blessing.