I started picking up the DVDs of this show at Blockbuster and have made my way up to the middle of Season 3 in the past couple weeks (this along with Sons of Anarchy is just about all I've been watching lately).
Good stuff. I love the almost Shakespearean, overly superfluous quality to the majority of the characters' dialogue, and Ian McShane's Al Swearengen is simply amazing. I've never liked a woman-abusing, foul-mouthed, son of a ***** pimp quite so much before now.
Robin Weigert's Calamity Jane is awesome as well, and Brad Dourif's Doc Cochran is a pleasure to watch.
The writing really is top notch. Its the kind of layered story-telling and characterization that forces you to pay attention to the story, and enriches it because of that.
I also love that while its fictional, it dips its toes into history both in terms of setting, plot, and characters. When seeing historical figures such as Calamity Jane, Wild Bill Hickock, George Hearst, etc, I'm usually interested anyway, being a history buff, but Deadwood delivers in all aspects. I also love the fact that the show is basically about how civilization and society forcibly arises out of chaos, how law and order have to be carved out of the wild.
Looking forward to the rest of Season 3.