I got into ASoIaF through the TV show and it fascinates me how differently I perceive the series to book fans. I've listened to a lot of the earlier episodes of APoIaF as well as some of the more recent ones and the reactions of that guy Chase seem to mirror that of a lot of GAFers - the urge to shout at the screen because of deviations from the source material appears to be a common factor.
As someone for whom it was a surprise to find out that Danaerys has purple eyes, that Tyrion was ugly, that the Baratheons had jet black hair and that everyone was younger than their on-screen counterparts, I find the changes people complain about to be trivial. Changes happen in any adaptation and my attitude is that as long as the players get to where they need to go and when, I'll give the makers the benefit of the doubt.
Was I disappointed when none of the Harry Potter films delved into the Gaunt backstory, but does it diminish the films? I would argue not on the basis that they are different media and there are more important things to get worked up about.
I do find some of the casting choices jarring on occasion, but that's just on account of the dissonance between my imagination and the actor and usually disappears upon seeing the actor actually perform.