I think for the most part 3e did a decent job of describing alignment with the exception that the writers didn't understand or make any distinction (in alignment terms) between self-centeredness and selfish.
By that I mean the statement, "Do unto others as you would have them do unto you." is self-centered, in that it depends on your own values and judgments to describe what you ought to do, but it is not selfish (and is in fact benevolent) because it encourages you to actively pursue the good of others from a frame work of self-centeredness. There is in fact even a criticism (very typically lawful) levied against the "Golden Rule" that since it is self-centered it doesn't work in the mind of a madman (or an Addams) who wanting evil things for themselves then does evil to others. Thus the proposal of the lawful version ("Platinum Rule") that says the same thing but centers not on the self conscious but on a hypothetical rational or moral individual. I don't propose to judge the argument here, merely note the relevancy to understanding what AD&D/D&D means by "alignment".
Likewise, the "Silver Reed" - "Don't do unto others as you would not want them to do to you" or perhaps "Harm no one; do as you will" - is also self-centered but not selfish, but in this case is not benevolent but passive as it focuses on the good of the self. There is of course a CN argument that focusing on the good of the self is the only good you can actually do, but again I don't want to pass judgment on that just point out the relevancy to understanding what AD&D/D&D means by "alignment".
This matters because when discussing what is meant by "Evil", 3e writers too often focus on the "Self" part of "selfishness" rather than on the destructive aspect of "selfishness" as the root cause of something being "Evil" which then leads to inescapable contradiction somewhere on the alignment wheel.
I would say this is no worse than Gygax's own bias who tended at times to favor "law" to the degree of seeing "Lawful Good" as meaning "more good" and "Chaotic Evil" as meaning "more evil", which is of course also inescapable contradiction. But it's still there and I'm not sure Gygax for all his brevity doesn't define the good/evil axis better than 3e writers do.