Someone recently made a very perceptive comment about Zelazny, which I'll repeat here: of his first two novels, This Immortal proved far more influential on his later work than did The Dream Master, and it might have been better the other way around. Immortal was jazzy, witty, and polished, but without much depth. The Dream Master was an elegant, substantial tragedy. The course he took later caused Judith Merril to ask, "Will Zelazny ever write the insides of his novels? Can he?"
He certainly didn't this time. Changeling is all around more satisfying than his previous one, Roadmarks, but still it has no insides. By way of improvement, it is a fairly complete story, which shows few signs of slapdash until the rather perfunctory end. It is not much ado about nothing, but the characters are sticks of wood.
Zelazny's powers of invention are working full force. The background is extremely good….
The problem is that Zelazny has overlooked the potential for tragedy. Instead he has written a light romp, like a very literate prose comic book. Mark, the one from the scientific world raised in the magical one, starts out as a decent, sympathetic type who is warped by hatred and misunderstanding until he becomes destructive. Even his "twin" tries to work out a reconciliation with him, but he is driven to his end. This is powerful stuff, but most of it happens offstage and out of the book. Remaining are a set of one-dimensional figures, Hero and Villain, and when the latter conveniently falls off a ledge at the end, it hardly seems to matter. There are moments of wit, and wonder, and even beauty beforehand, but they don't add up to much. This is only an average quality novel after all. I'd rate it a C+.
Darrell Schweitzer, "Book Reviews: 'Changeling'," in Fantasy Newsletter (© 1980 by Paul C. Allen), Vol. 3, No. 10, October, 1980, p. 6.