I'd been waiting for S4 before forming a conclusive opinion on this, but now - having recovered from the disappointment of S4 - I'm sure The Great Game is the best episode (i.e. my favourite) of the show. It is subtly layered, extremely intelligent and almost flawless. I'm usually the nitpicker and can spoil the fun for nearly anyone by pointing out flaws in a movie but The Great Game really encapsulates everything that's great about the show.