Yorke’s voice is an unrelentingly beautiful thing that sometimes bothers him for precisely that quality. He sings in a strong and aspirate voice, and favors legato phrasing. His pitch is sufficiently accurate so that he uses vibrato only when he needs to—as an effect that can be drawn on for any number of aesthetic reasons. His singing is so pretty that Radiohead can sometimes lack the aggression that is a crucial aspect of much rock music, especially the average kind.
Sasha Frere-Jones in a nice piece on Thom Yorke/Atoms for Peace