Here is the relevant passage:
...I am absolutely opposed – adamant isn’t in it! – to a TV version. Anthropomorphic animals, when taken out of narrative into actual visibility, always turn into buffoonery or nightmare. At least, with photography. Cartoons (if only Disney did not combine so much vulgarity with his genius!) wld. be another matter. A human, pantomime, Aslan wld. be to me blasphemy.I think what Lewis is objecting to is the grotesquery of portraying the godhead in pantomime. I feel rather certain that Lewis would never object to the convention of of the masque, or to the portayal of the godhead in passion plays. It is the pantomime that raises his ire.
However, Lewis seems to feel that animation would be an acceptable. And how is Aslan portrayed in the upcoming movie? Digital animation.
I think that Lewis was very close to correct when he uses the phrase "buffoonery or nightmare." I have seen the trailers and, while I saw no buffoonery, the moment when the wolf turns to the camera and speaks is going to be nightmare fodder for many children.
Of course, years from now, small children will see this movie and smile to themselves at the simplicity of the animation, wondering how mother and father could have been at all upset. But the first generation of children seeing this movie in theaters are going to be profoundly impressed by this telling of Narnia.