I think what makes Iwan good as Ramsay is that he plays him kinda like Andrew Scott did Moriarty in Sherlock BBC. All crazy-eyed and unhinged, it can be quite good at times, and an empty yet pretty shell at others, for Iwan.
I don’t mind Iwan as Ramsay, but he’s not what I pictured, you know?
I think 50% of my comments regarding his portrayal have to do with the construction of the character. The writing hasn’t paid respect to the source, so it’s slightly a different character. More cardboard cut out than his book counterpart (not his fault clearly). And the other 50% has to do with his acting. I don’t think he’s bad, I think he was ok, but in general he doesn’t inspire fear and creepiness, like book Ramsay did (it’s an image-look thing matched with body language. Not his fault he doesn’t have it). There's still something meh about his portrayal, that has to do with nothing else but his acting. Still is early to give a definitive opinion on it, because most of the Ramsay-Theon storyline happens later on. I just hope they don’t over do it, because at the end of season 3 it felt that way.
And I like Iwan. He was good in Misfits. And I definitely think why they cast him, and why they think he has the elements to portray Ramsay.
Will trust your word on the Moriarty comparison.