The Craftsman's Delight
And God saw everything that he had made, and behold, it was very good. (Genesis 1:31, ESV)
In Genesis 1, God calls his Creation "good" six times, one for each day of Creation, and then finally says that it is "very good".
But what does God mean exactly by "good"? This is something that, perhaps, we all understand intuitively, but it becomes less clear when we try to precisely define it.
The usual thing to do, for Bible scholars at least, is to find the Hebrew word and take it to a lexicon (dictionary). The Hebrew word for "good" is טוֹב (ṭōv). In this case, that approach is very difficult, because like our English word "good", the word טוֹב has many slight variations in meaning. HALOT lists at least nine different meanings, and about five of those, at first glance, seemed like they might plausibly fit the context of Genesis 1. I went through many of the lexicon references, but saw there was much imprecision and overlap in the categories, with some references actually appearing in more than one category.
To make a long story short, it seemed more useful to focus on finding a specific individual usage of טוֹב that seemed to parallel well the context of Genesis 1. The verse I settled on was Isaiah 41:7, with the ESV translation quoted below:
The craftsman strengthens ("encourages", in some translations) the goldsmith, and he who smooths with the hammer him who strikes the anvil, saying of the soldering, "It is good" (טוֹב הוּא, ṭōv hū); and they strengthen it with nails so that it cannot be moved.
The context is that some heathen craftsman are assembling an idol, which they hope will help save them from a coming conqueror. Of course, that is not what is happening in Genesis 1. Nevertheless, here the craftsman observes the work of the goldsmith, and sees that the soldering has been done well, and is satisified that the job is done well enough to move on to the next step of assembly (fastening it with nails). Those who like to build things will understand the craftsman's satisifaction and even delight when a product turns out well.
In Genesis 1, God serves as His own quality assurance team, and is satisifed and delighted with his own work. After each day's work, he sees that the product of his work has turn out well, and is fit for the next stage of Creation. And at the end of the sixth day, he declares that his completed work is "very good" (טוֹב מְאֹד, ṭōv mᵉ-˒ŌD).
In Genesis 2:18, God declared that "It is not good that the man should be alone" (ESV), indicating that there was something in his Creation not (yet) satisfactory and in order. Of course, God is not forgetful or making mistakes — he does this to put emphasis and honor on the creation of Woman.
I do not believe, strictly speaking, that טוֹב is being used here in the moral sense (e.g., "he is a good man") but it is certainly implied that God's Creation was at this point free from evil, or else God could not have taken full delight in it and called it "very good".
 Curiously, God does not call Creation good at the end of day two, but does so twice on day three. Dr. Gill mentions that some interpret verse 9 as "God had said" to bring the events of vv. 9 and 10 back into day two.
 Some translations (e.g, NLT, Douay-Rheims) suggest a slightly different order of events in this verse, but I don't think that would substantially affect the parallel I am drawing out.