I caught the most recent series on iplayer after I heard the praise given to the Shakespearean episode, and so watched the rest of series 4 pretty quickly. I've also just found some of the earlier episodes on Netflix and so have started to binge those as well.
Been watching it for a few years now, seen every episode except the very first one I think. It's a superb show, doesn't always strike gold but even the lesser episodes are structurally well put together. One of the few things that can still surprise me.
Yeah, one thing I've been enjoying is the storytelling, the way most episodes seed the information you need and how it all relates to the pay off at the end.