I don't think the racism is that bad. The characters themselves are quite racist and there are some pretty broad stereotypes, but there are good and bad folk of many races and colors, as I recall.
Early in his career, Howard did write stories that were openly racist. By the time he was writing Conan, however, his views on the subject had evolved. If you stick to his Conan stories you'll not only find little or no racism, but, as pawsplay says, you'll discover all races possessed equally of grandeur and baseness.
As for shameful- I agree with you in all cases but one. The Vale of Lost Women is about as starkly racist, misogynist and homophobic as Howard gets, and in that case, he gets pretty damn far.
It's been a long time since I read that particular story, and I'm not sure I've ever read it in a non-expurgated edition. But my memory of this particular story is that it's told from the POV of a female character who views the world through the assumption that all men are misogynistic and dark-skinned people are beasts. This POV, however, is explicitly criticized through the words and deeds of Conan (who treats the black-skinned men as equals and wasn't actually going to do all the misogynistic things she assumed he was going to do). In fact, the entire point of the story seemed to be about how wrong-headed her POV. In many ways, I felt that it could be read as a direct critique of similar wrong-headed ideologies being portrayed in pulp fiction.
But, as I say, I haven't read the story in years.
With all that being said, Howard was certainly a product of his time. His understanding of history, for example, is heavily tinged with concepts like "racial migrations" and the like. This lends Hyperborea a certain epic scope, but the language has unfortunate associations to the modern ear.
Of course, if you're the type of person who becomes offended when an historical work refers to "negros" instead of "African Americans", then you'll find plenty to offend you in Howard's work.