He's so young! 24 or 25, playing a very convincing 17-year-old, broken, manipulative, pitiable, and scary by turns--and occasionally all at once. Voice pitched higher than I'm used to hearing (to the point where I'm not sure I would have recognized him by voice alone, which I'm quite good at normally); only a couple of times did I think "there's John!" such as when he did that sly/bemused half-smile that I'm so used to seeing from Sam Tyler.
The more I see of his work, the more impressed with him I am. I'd love to write a script for him someday, see if I can't give him something to work with that he hasn't tried yet (I have this weird desire to cast him as an Anglican priest, but no story to go with it yet).