I agree with Fungasite pretty much entirely. Good and evil are important concepts and are worth the trouble of making coherent.
Law and Chaos, OTOH, seem severly incoherent to me. This is thrown into clarity when one considers what characteristics one attributes to law and chaos:
Law:
Order
Positive Law
Stasis
Inflexibility
Civilization
Rule of Law
Knights
Dwarves
Adherence to tradition
Personal Honor
Truth-telling
Collectivism
Discipline
Cynical Politicians
Chaos:
chaos
Entropy
Flux
Lawbreaking
Barbarism
Barbarians
Case by case decision-making
Rule of people (as opposed to rule of law)
Lying
Adherence to tradition (as opposed to positive law)
Personal Honor (again, as opposed to positive law)
Elves
Disorder
Anarchy
Individualism
Free Spirit
Noble Savages
I'm sure that there are a lot more attributes that other people can think of but all of the ones I've mentioned seem pretty clearly associated with Law and Chaos (with the possible exception of lying). If you break them down, there seem to be several categories:
Cosmological/scientific: Order/chaos, stasis/entropy, flux, or change.
Political: Rule of Law/rule of individual, Rule of Law/Case by case decision-making, Civilization/Barbarism, Positive Law/Tradition, Positive Law/Personal Honor, Collectivism/Individualism, Order/Anarchy
People Groups: Knights/Barbarians, Dwarves/Elves
Personal: Adherence to tradition/Individualism, Discipline/Free Spirit, Personal Honor (knightly)/individualism, Adherence to the rule of law/concern for personal honor (barbarian-style "city men have no honor and therefore lie and cheat one another")
The problem is that many of these oppositions and concepts have nothing whatsoever to do with each other (note, for instance the number of times personal honor appears on both sides of the various oppositions and the various cosmological principles are pretty much all undesirable and, in any event, have nothing to do with one's position on the rule of law or collectivism vs. individualism) and others are actually mutually exclusive (for instance, rule of law is a necessary component of an individualistic society).
Since there's no apparent unifying concept (other than D&D alignment which isn't at all helpful) to tie these disparate ideas together, it doesn't make any sense either as a description of a character (is my honor-obsessed noble savage barbarian who wishes to preserve the traditional ways of his people unchanged lawful or chaotic?) or as an evaluation of a character (what, exactly is being evaluated?)
Good and evil, while far too basic to be a full description of a character are still significant and important as evaluations of a character--something which seems like a major element of the mythic worldview that I want D&D to model.