Or HaChaim on Numbers 11:10/אור החיים על במדבר י״א:י׳

1 ויחר אף ה׳ מאד. G'd's anger was kindled very much. The reason why the Torah describes G'd's anger as מאד, "very much," is that people who fall victim to seduction by Satan have been victimised, in a sense. The same could not be said of the people described in our paragraph who had actually provoked the evil urge within themselves. There is no category of sin which is greater than that.

2ובעיני משה רע, and it was wicked in the eyes of Moses. Man is upset if something he considers his own creation does not live up to his expectations. You may find an illustration of this when the prophet Samuel is reported as having aged prematurely and died as a result of the anguish of seeing King Saul whom he had crowned not having met the challenge of wiping out Amalek. In order to save Samuel from experiencing Saul's death at the hands of the Philistines (compare Taanit 5) G'd had him die prematurely. Moses too was upset at Israel acting in a manner not befitting them. Alternatively, we may understand the words ובעיני משה רע as referring to G'd's anger. It displeased Moses that G'd had become so angry at the Israelites on this account. According to Sifri 1,95 G'd gave Moses a preview of the punishment He was going to exact from Israel on account of this misdemeanour. Moses reacted by asking G'd whether He really considered it fair to feed the Israelites meat only to let them die as a result of their eating the meat.