This is such a difficult work that even Dummett's The Logical Basis of Metaphysics seems trivial in comparison. 350 pages of torture. Whitehead's style is also not inviting at all. He had already written the Principia by then. The last of the grand old metaphysicians. Deleuze seems nothing compared to him.

"Its influence will radiate through concentric circles of popularization until the common man will think and work in the light of it, not knowing whence the light came." Factually the whole second half of the 20th century was under the influence of Whitehead, in the guise of Gaia hypothesis, ecology, embodied etc., though extremely indirect, and along with other factors like Jungian, Teilhardian thoughts. Ingold's anthropology, phenomenology after Merleau-Ponty, the hype with Buddhism... All stems from this monumental, epoch-making work.

If you read Schelling, or Jung, or whatever process theology, Whitehead is a must, since he's a developed form of Schelling, and was influenced heavily by Schelling. Don't read those process philosophers who are largely influenced by ecology and the counter-culture of the 60s and 80s. Read the master directly. It's a pity that Whitehead was popularized by Americans.