The following article, by R' Yosef Avivi, appeared in Gush's "Daf Kesher" for parshat Hukat this year. I found it interesting, and here is a quick and dirty translation.
Jewish philosophy in recent generations has been based on and formulated through Kabbalah. The Ari's Kabbalah is the source and fountainhead from which the philosophies of Ramchal, Baal Shem Tov, and R' Kook flow. These three, though they differ in location and time, are close to each other in logic and approach. All three interpreted the Ari's Kabbalah, and their interpretation forms the interpretation of their thought and the originality of their approach. Their common base - the Ari's Kabbalah - is hidden and impenetrable to the point that any commentary on it is a new, independently standing creation. The Ari's Kabbalah was formulated according to "hidden" wisdom - sefirot and partzufim, emanation and regression - and its interpretation consists of its formulation according to revealed wisdom - ideas and logic, principles and means of thought. The common source of the three interpretations reveals their commonalities and differences, what each thinker innovated and how he interpreted the Ari's Kabbalah.
In a few lines I wish to describe the innovation of each thinker. I will not detail the basics of his thought, rather, I will try to extract what each of the three innovated - Ramchal, Baal Shem Tov, and R' Kook.
The Ari taught that the sefirot were emanated as light and vessels. The vessels were broken and the light fell and dissipated; afterwards the sefirot were repaired and the light appeared in new repaired vessels, but there are still broken vessels with sparks of holiness in them, in need of repair. Israel's labor in Torah, prayer and mitzvah performance forms the repair of the vessels and elevation of the sparks, until complete repair of all the worlds is reached. Later scholars came and explained what is meant by repaired sefirot and by broken vessels with sparks of holiness in them; what has been repaired and what needs repair. The description of these two realities is the essential innovation of each of the later kabbalists in their interpretation of the Ari's teaching.
Ramchal explained that the sefirot are details of God's governance of the world. Everything that is described about sefirot in all their varieties is a prophetic vision in which God shows Israel how He governs them and the world. The various sefirot are His various attributes. Ramchal introduced the idea that the light and vessels are two forms of Divine conduct: the light - the conduct by which God's unity is revealed, through which God's holiness and goodness are revealed and it is revealed that there is none other than Him. And the vessels - conduct by which human free will, reward, and punishment are revealed. Humanity's task - revealing the light which is the conduct attesting to Divine unity, and repairing the vessels which are the conduct attesting to reward and punishment. These are accomplished through keeping the Torah and commandments, and through hope and expectation for the appearance of Divine unity.
To summarize the Ramchal's innovation: The border of the world of emanation is what needs repair - i.e. the complete appearance of unbounded light in it.
The Baal Shem Tov saw the sefirot in the human soul, and interpreted Heavenly conduct according to the behavior of the human soul. The Baal Shem Tov laid the foundation for this perspective, and the Baal Hatanya built the entire structure. Intellect and character traits, enthusiasm and vitality are the activities of the sefirot and the changes in their status. Thus, on a high level, "from my flesh I shall see God". There are two souls in a person - Divine and animalistic; and thus a person's task is to cling to God with both his souls.
To summarize the innovation of Chassidut: The animalistic soul and a person's secular activity need repair - i.e. the manifestation of holiness in them through clinging to God.
R' Kook saw the sefirot in the world of trends, theories, and ideas about life and their application. There are two worlds: the holy world begins as a world of Divine trends and aspirations, free without constriction or boundaries, and ends with their contraction and bounding to human dimensions, while remaining in the freedom, Godliness and absoluteness. The secular world begins as a world of human trends and aspirations, natural and bounded, and ends with their self-destruction [?] and and mutual struggle until the evil [?] is apparent in them. Therefore humanity's task is to raise the secular world to the holy and to make fully revealed the holy light.
To summarize R' Kook's innovation: All natural-human ideas and ideals and the ways of life that follow from them - are secular, and need repair, i.e. the appearance of the Godly ideals and the holy world that is in them.
We see that what the Ari said about the world of emanations, of degradation and repair, is interpreted by the Ramchal as behavioral patterns in Divine rule, by Chassidut as behavioral patterns in the human soul, and by R' Kook as patterns of life customs.