Can someone explain "Noble Eightfold Path" in depth?

The whole of the Noble Path can be summarized as the action, speech, effort, intent etc. coming from the two kinds of thoughts as explained in MN 19:

Bhikkhus, before my enlightenment, while I was still only an unenlightened Bodhisatta, it occurred to me: ‘Suppose that I divide my thoughts into two classes [-- useful and harmful].
...
As I abided thus, diligent, ardent, and resolute, a thought of [the harmful kind] arose in me. I understood thus: ‘This thought [of the harmful kind] has arisen in me. This leads to my own affliction, to others’ affliction, and to the affliction of both; it obstructs wisdom, causes difficulties, and leads away from Nibbāna.’
...
As I abided thus, diligent, ardent, and resolute, a thought of [the useful kind] arose in me. I understood thus: ‘This thought of [the useful kind] has arisen in me. This does not lead to my own affliction, or to others’ affliction, or to the affliction of both; it aids wisdom, does not cause difficulties, and leads to Nibbāna.

Briefly, my personal opinions / commentary.

Arya marga. Here, "arya" ("noble") stands for "advanced person" and "marga" ("path") stands for "training method". Together it means "The advanced person's training method".

Each of the eight points starts with the word "samma" (Sankst. "samyak") - "right", which in this case means "high-quality", "adequate", "effective", "useful" - in bringing about the good results.

• The right view (or useful philosophy) stands for one's perspective on life in general.

  The central point of the right view is that our life can get better (away from afflictions & difficulties and towards wisdom & peace) or worse (away from wisdom & peace and towards afflictions & difficulties) -- depending on the choices we make. The subsequent points build up on this basic idea.

• The right intention (or useful attitude) stands for one's attitude as one goes about life.

  Right intention is trying to improve things, not to harm or make things worse. It is a deeply constructive attitude, not a destructive attitude.

• The right speech (or useful speech) stands for one's skill in interacting with others.

  Basically, it is speech of a wise person who knows what to say, how to say, and when to say it in order to achieve well-being for oneself and others.

• The right action (or useful behavior) stands for one's self-control in acting strategically and not impulsively.

  As with the rest of the points, the idea of right action is to not do anything (stupid) that will have an adverse effect, but to act skilfully in order to maximize the net benefit, esp. long term. The useful behavior is characterized by sobriety, discipline, moderation, and making wise choices about what one is getting into and with what kind of people one is connecting one's destiny. The useful behavior comes from the thought like "what kind of long term result will I get if I do this?"

• The right livelihood (or useful lifestyle) stands for the circumstances and environment one chooses or agrees to live in.

  Useful lifestyle is a lifestyle more or less supportive of the useful thoughts and useful actions towards a good result -- not a lifestyle that forces one to go in a completely opposite direction.

• The right effort (or useful effort) stands for self-improvement.

  Specifically, it means the ongoing effort to stop and get rid of the pathological habits/impulses/hangups, and to develop the "right" (useful) skills.

• The right mindfulness (or useful frame-of-reference) stands for watching for the two kinds of thoughts as one goes around the day.

  The idea is to not let oneself be carried away by the pathological currents, but to go around one's day while staying within the perspective of arya marga.

• The right concentration (or useful mood) stands for one's ability to control one's attention and therefore one's perspective and mood.

  The point of right concentration is to stop being the slave of information and to become the master of mind.

In short, in our day to day practice we must have a good sense of direction -- which way is feeding our ego and weaknesses, and which way is being an "arya" (advanced person). Your know your efforts are correct if you become less frustrated and more successful with whatever you do.

Because Sat-Dharma is "good in the beginning, good in the middle and good in the end", the Noble Path works on all levels:

• On the mundane level it helps one achieve success and better quality of life through developing self-control and discernment for constructive strategic action.
• On the personal level, it guides one towards overcoming neuroses, attaining the mastery over one's emotions, and achieving a stable & happy state of mind.
• On the social level, its emphasis on overcoming the harmful impulses, developing self-control, and the focus on constructive positive action - encourages cooperation, harmony, and seeking a compromise for the greater good.
• On the intellectual level, it encourages intellectual agility, open-mindedness, and anti-dogmatism as necessary conditions for skillful response.
• On the level of the spiritual quest, it provides a working framework and a practical way of gauging one's progress for abandoning obstacles on the way to Enlightenment - from overcoming coarse emotions, to dismantling the ego, to uprooting the preconceptions, to realizing the nature of mind, to attaining prajna-paramita.