I think they've told it as it was told in the books for the most part. He's depicted as every bit the the worthy successor to Ned in the TV show too. He just happened to make one very big, very stupid mistake.
Not for me, but there seems to be different opinions on this topic; so I guess the TV writers haven't done such a bad job after all.
Quick poll, when did people last read ASOS? Cause i think how fresh in your mind the books are plays a big part in your enjoyment of the TV show. Least it did for me last season.
Read it 4-5 years back; read the first 4 books in relatively short time span and kept twiddling my thumbs for the 5th one (which was a major let down considering the wait). I have actually quite moved away from the series and wouldn't be too fussed if the series doesn't end.
Regarding turning viewers away, yeah, I too think that won't happen. I just thought they will put Joff's wedding as a sweetner in the same series. Personally, I will be gutted when Joff turns blue as he is one of my favourites in the TV series.
Also, does anybody think that Blackfish will have a bigger role now that he has been introduced? All his exploits were pretty much as Robb's advisor which were glossed over. Wonder whether Blackfish has a big role in the upcoming books.