I cannot think of a better Joffrey than this guy. Personally, this is the first show I have seen him on it but I'm impress on how he pulled the royal brat to the core. Watching him made me feel anger and frustrations which only means he delivered a good performance. He is so good that I to slap him as well, bravo on the acting chops.
From reading the books and seeing Gleeson's portrayal on the show I gotta say he did good. I genuinely despise the kid now. No matter what else he plays in he will always be that asshole Joffrey to me. So he's done well in the series so far.