Greed has one, fundamental, flaw. It is a tragic flaw that eclipses all his other attributes. It is the flaw that ultimately led him to defy his creator, his master, and betray his brethren. It is the flaw that caused him to be sealed for over a hundred years.
Now he is free of the seal, but not of his one, fatal flaw. And as he looks into the face of the child that will be his murderer, Greed realises that this one flaw will kill him.
Envy was right. He really is far too nice for his own good.