In the past couple of months I have read/ listened-to a dozen Philip K Dick novels, and most of the Exegesis - his philosophical and spiritual journal written during his last eight years. I haven't enjoyed a fiction writer so much, in such quantity, for several years. Certainly, I appreciate his work more fully this time round than when I read a batch of his novels more than thirty-five years ago (triggered by watching Blade Runner - one of the half-dozen best movies I've ever seen).
Although there are several of his important works still to go (I'm 'simultaneously' reading three of them at present) I think I have by-now achieved a reasonable overview.
In particular; I have noticed that his very best novels are from the 1960s, and before the spiritual revelations that began abruptly in February and March 1974, continued through the rest of his life - and led to his almost daily and extensive work recorded in the Exegesis - which was the attempt to make sense of what was happening to him, and understand the implications.
It seems to me that the novels published after 1974 are mostly interesting and worthwhile (especially VALIS), but they lack the fluency and coherence of Dick's best 1960s novels such as Man in the High Castle, Dr Bloodmoney, Three Stigmata of Palmar Eldrich, Do Androids Dream of Electric Sheep, Martian Time Slip and Ubik. In particular, the final two novels - Divine Invasion and Transmigration of Timothy Archer - are not satifying as a whole, and have a certain flatness and lack of empathic characters.
My conclusion is that Exegesis was receiving PKD's best efforts, and the attempts to spin-off novels from it were contrived, over-planned. VALIS is something of an exception, being composed of lightly fictionalised 'excerpts' from Exegesis - however, I did not find the ending satisfying, and I enjoyed the unselfconsciousness and energy of the original, more than the same material when put into fiction.
I feel that VALIS - by means of the literary conceits of its structure - erects a barrier of 'deniability' between the material and the reader. In particular, in all of Dick's last three works, the possibility of a genuine contact with the divine is put into brackets, and the materialist explanations seem to triumph overall. Whereas in the Exegesis, the most high intensity and ecstatic sections are without doubt those when PKD knows (albeit temporarily) that he has had real revelations of the truth.
Dick's mainstream critics and admirers, and most of his social circle, are normal modern Leftists for whom the divine is excluded by assumption; and who therefore necessarily interpret every strange experience as generated by insanity, drug use or over-imaginative wish-fulfilment.
(From what I have seen, so far) Perhaps only his friend, the author Tim Powers (a Roman Catholic) was able and willing to acknowledge that what Dick experienced included genuine divine revelations. And only when this possibility is recognised, can the Exegesis be appreciated as fully as it deserves.