What a good comment is? One that eases the understanding of a block of code.
What a good code is? One that does not requite any comment to be understood.
EDIT: As the brevity of this post seemed to cause some confusion, I'm not advocating the no comments practice. That's only lazyness. Even literate programming for me is nice (but I would not use it in a commercial project), the point is, you should comment every non-trivial issue, and you should code in a way that makes most issues, trivial. (bad) example follows:
// good comment bad code:
assetmanager.loaddata(filename, true); // async load of player mesh
// good code:
// good code, good comment:
assetmanager.load(playerMeshFile, MODE_ASYNC); // preloading data in the frontend, as the user has already choosen its player