In 4th edition, good characters are those who believe that protecting and helping those in need, or those who are too weak to act for themselves, is the right thing to do, without special regard for the law or authority. The good alignment includes tenets from the neutral good and chaotic good alignments from previous editions.
The good alignment is distinct from the lawful good alignment in that good characters are not bound to sacrifice themselves or ignore completely their own needs for the sake of some ethos or code of conduct, although they probably have a strong inclination to do so. They are aware that power corrupts those who wield it, and that it's better for authority to rest in the community rather than the hands of a single individual. Good characters fight the law when it becomes exploitation.