In a sea of "Zen/Zen Buddhism" manuals and guides, this small work manages to stand out. There ends up being a lot of repetition in texts on Zen - every writer/expert/sensei et al. feels they have to re-hash the same key phrases and anecdotes. Or we are given yet another interpretation of very familiar koans or quotes. However, THIS text somehow stands out among all the heaps of others.
The thing that makes this work unique is, I think, the clarity with which the author wrote. He very nicely bridged the gap between esoteric personal experience and the universal experience of Zen. He also very carefully wove these teachings in and around modern religious zeitgeist. Its not overdone, it is very subtle. But the insights here are not belligerent or evangelical, and are probably the most inclusive I've seen in any religious writing in awhile.
Two concepts most emphasized in this are: enlightenment takes lots of work (Cp. Rinzai) and there is a oneness.