Written 12 years before One, Illusions has been instrumental in the spiritual development of numerous people, one friend in particular. His interest led me to read it, which then led me to write this review (critique, commentary, whatever).
It's more didactic than ONE: the primary thesis that he pushed was that our fate is the consequence of our choices. That idea contains much truth, but it can be pushed too far.
(I once moderated a Great Books discussion about some topic having to do with our responsibilities to one another. In the group a man who must have been a prosperous and fairly radical libertarian dissented from the idea of social welfare and said that no one had ever done anything for him . I lost it right there and asked him if he'd ever gotten any milk from his mother's breast--short career as moderator!.)
I felt that Bach pushed it too far; he presents his credo in the beginning, in which a Master come to earth said unto them, "within each of us lies the power of our consent to health and to sickness, to riches and to poverty, to freedom and to slavery. It is we who control these and not another".
That contains some truth, but it also cries out for abusive interpretation: if I manage to deprive you of your wealth, your liberty, and to enslave you, that was your choice. Sorry, I can't buy it.
The theology of Illusions does not have room for love, which IMO is the ruling power of the Universe. Love seemed to be hard for Bach; he celebrated passionate love in ONE, but his passionate love seemed to have passed with time.
"If it looks like wisdom, but is unkind rather than loving, it's not wisdom.
If it feels like love, but it's not wise, it is not love" (page 149 of Awakening The Buddha Within by Lama Surya Das.)
Bach does have much wisdom, which indicates that love lies within him, though perhaps disguised, even from himself. In him I see a man running, no, flying from The Hound of Heaven; he looks nervously over his shoulder and knows that he's going to lose the race.
(I welcome dissent, even utter complete disagreement. It's refreshing. Please do.)