CS Lewis, CS Lewis...oh boy!
You spoiled a great chance for writing an amazing novel here.
You showed amazing skills here, but then you decided to put them off, giving up what you began. You started something you couldn't finish.
I don't know if the first two books of this "Space Trilogy" of yours are better or worse than this third chapter.
What I know is that in "That Hideous Strength" you were able to sketch loads of promising issues finding an enviable balance in the clockwork crescendo of the first pages. But then, someone or something switched off the light. And the whole house of cards collapsed.
Should I blame that often vituperated "Christian element" which appears to be the slant for interpretating your literary production? I don't know. But I wonder.
This book had it all: dystopia, an evil organization that want to rule the whole humanity being led by a guillotined head, the resurrection of Merlin, social satire over the academic world, a sort of interstellar angels whose name sounds like whispered to your ears by your buddy JRR himself. And last but not least, we meet the heir of Uter Pendragon who would like to come back to planet Venus where he spent such an enjoyable time. This Earth must be so boring if you are immortal.
At some point dwarves, pixies, lions and even a playful bear named Mr Bultitude appear while the lack of a Babelfish is deeply missed at an important luncheon among those who aim to rule the world in a NICE way.
Well these premises given, my dear CS, you failed.
Where is the long-awaited battle between good and evil, between the modern "scientific" world and the ancestral gods of old Britain you evoked? What happened to the crucial clash?
Neil Gaiman have done it better with "American Gods". In fact the two books have very much in common. But the pupil overcome the teacher, fifty years later. What a pity. You saw it first, but didn't make it.