I respectfully disagree with the OP. By all means, don't watch the series if you want to avoid sex and violence. Those are going to exist in any adaptation of
A Song of Ice and Fire. But please don't say the characters have no redemptive qualities (due to full frontal nudity, apparently) based on your objections to the content.
The series is relatively dark, but the characters are human. Plenty of them are bad people, yes. But others are noble and many have simple human motivations that lead them to do things both bad and good. Though the series is not completed, based on the four books so far I can say that it is definitely a notable fantasy which pushed forward the worldbuilding of cultures and families.
ShiroiHikari wrote:So has anyone here actually read these books? Is the "mature content" just arbitrarily added or is it in the source material too?
I can't watch the series due to location, but from what I've heard it's a fairly faithful adaptation (just simplifying things and changing the order around). There are really only two major sex scenes in the first book (as in ones that could not be removed without changing the entire plot), one of which would probably have been in the first episode. HBO could probably show sex where the novel only implied or referenced, but I doubt they'll be adding it just for fun.
Really, though the series does have feature sex, it's neither as frequent nor as explicit as in many other fantasy series written for adults. What ASOIF does have is a fair number of crude characters and references to sex, so if that bothers you then you should probably avoid it.