I think roger has a very decent singing voice. Near the end with the Floyd it was rather emotive and personal, and the persona of his concept ideas were people disillusioned from the world, hence the crabbyness and excessive screaming. I agree its not the best voice, but it is unique..much like Pearl Jam's ed vedder...you always know when roger is singing

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...there's no dark side of the moon really,...matter of fact its all dark....