The acting was generally very good, and a particularly pleasant surprise was the numerous child actors who did sterling work. Joffrey was as repellent as he ought to be, Arya was a very likeable tomboy, and Sansa was naïve and full of herself. Naturally, Sean Bean gave a bloody good performance as Ned Stark, (almost the only honest man in King’s Landing). Peter Dinklage played Tyrion Lannister, and was also thoroughly excellent.
There was more sex than expected, and a reasonable amount of fairly graphic violence. It wasn’t overdone but it’s clearly not family viewing or for the particularly squeamish.
The plot is very close to the book and the differences are largely there for reasons of practicality (there’s a normal carriage rather than a massive one for Cersei) or clarity (the Others are referred to as White Walkers throughout). They’ve had to slightly tone down one or two things (I forget how old Daenerys is in the book, but I think she’s a bit older in the TV series) but not much.
There are a range of extras, including commentary on many episodes (from cast and crew), background on Westeros and character profiles. The first commentary is by a pair of producers, and was actually pretty interesting (well, I thought so). So far I’ve only listened to that and the second commentary, with a trio of actors (Headey, Addy and Coster-Waldau), which was also enjoyable.
I think the TV series does the book justice, and A Game of Thrones is one of the best books I’ve ever read. There’s a second series due to begin on TV soon, and I hope it’s as good as the first (and that the DVD gets released a bit sooner this time).