What is the significance of the Torah's description of the Manna to coriander seeds and to crystal?
Rashi: The Manna was (pleasantly) round like a coriander seed and sparkled like crystal.
In what way do the current Pesukim constitute a complaint?
Rashi: Although the previous Pasuk presents the people's complaint against the Manna, the current Pesukim come to present Hashem's answer to the complaint - and it goes on to describe the beautiful appearance of the Manna and its other positive qualities 1 - When it came down it was round (or white), 2 and when it was ready to eat (or when it turned hard), it sparkled like crystal (Targum Yonasan).
Rashbam: They constitute a complaint, inasmuch as they describe the physical features of the Manna - hard and dry, rendering it inedible, like dry wheat. 3
Rashi: To show the world the futility of His children's grumblings. See also Targum Yonasan.
See Na'ar Yonasan.