Peter Pike claims that I haven't done the job of defining goodness. Let's have a look at his own attempt to do so.
1. God exists with certain attributes that make up His nature.
2. God's nature determines how He acts, what He wills, etc.
3. God gives general commands to us, based on His nature.
4. God is immutable.
5. Logically, then, God's general commands will not change. They are what they are.
I argue that for us good is doing what God commands us to do, and evil is not doing so (including acts of comission or omission; that is, doing what you shouldn't do or NOT doing what you should do are both evil).That means we only have to concern ourselves with the commands of God.
At the risk of becoming tiresome, I would have to ask what definition of God we are working with here? If God is a being omnipotent, omniscient, and perfectly good, then but something is good if it is in accordance with the commands of God, we have a problem.
In my view moral obligation is created by the fact that God creates us with an intended purpose which is identical to our good, in that we as humans flourish if we fulfill that purpose. Further, God acts in a way that is consistent with the pursuit of that good for all his creatures. Our good is to glorify God and enjoy him forever, evil is what gets in the way of that.
On Calvinist theory there is a large gap between what makes God's character good, and what makes us good, a gap that cannot be explained in terms of a difference in God's wisdom or knowledge. A native may believe that men in white coats bearing long needles are mean to little kids because he lacks knowledge that the men in the white coats possess, but the standard of goodness for natives and for missionary doctors is the same. Both the native and the doctor want the child to be well, and for the child not to suffer, but they have different ideas as to how to go about it. Piper seems concerned to respond to the charge that God's interest in his glory makes him selfish, since selfishness is a vice amongst humans. If I were to read on someone's tombstone "He pursued his own glory single-mindedly throughout his life" I don't think I would think I was looking at the grave of someone I wish I had known. Glory hogs in basketball don't help the team win.
It seems to me that when you say God gives commands based on his nature, it is pretty clear that we don't have obligations to reflect all aspects of God's moral nature in our own conduct. We might be rightly wrathful when someone we love is raped, but we aren't supposed to be looking for or artifically creating opportunities for us to exercise our attribute of being wrathful at evil, (maybe by creating androids who commit crimes so that we can punish them for those crimes) as if there was some aspect of us that is going to go unfulfilled if we are fortunate enough never to be in a position where that sort of wrath is called for. So while divine commands are supposed to be based on the divine nature, the kind of people we are commanded to be fails to fully reflect the character of God, and there are actions on the part of God which are deemed right which, if parallel actions are performed by humans, they would contravene the commands of God.