Ramban

AND, BEHOLD, IT WAS VERY GOOD. This signifies their permanent existence, as I have explained. The meaning of the word me’od (very) is “mostly.” On this sixth day He added this word because he is speaking of creation in general which contains evil in some part of it. Thus He said that it was very good, meaning its me’od is good [thus conveying the thought that even the small part of it which is evil is basically also good, as is explained further on]. It is this thought which is the basis of the saying of the Rabbis in Bereshith Rabbah: “And, behold, it was very good. And, behold, it was good — this refers to death.” Similarly the Rabbis mentioned, “This means the evil inclination in man,”, 9. “Were it not for the evil inclination, no one would build a house or marry a woman.” and, “This means the dispensation of punishment.” “He considers well how to mete it out” so as to cause a minimum of suffering. Onkelos also intended to convey this thought for he said here, “And, behold, it was very orderly,” meaning that the order was very properly arranged since the evil is needed for the preservation of the good, just as it is said, To every thing there is a season, and a time to every purpose under the heaven. Some Rabbis explain that on account of the superiority of man, He added special praise on his formation, i.e., that he is “very good.”