As far as DEADWOOD goes, curious to know if you've checked out the new movie? I've not seen it yet, but being on the very of having viewed the entire run of LOVEJOY, it's amazing to contemplate McShane having played such amazingly disparate roles.
On the other hand, perhaps the role was pitched to him as "Al Swearegen: He's Lovejoy without the antiques, but with, well, a lot of swearing!"
I do pretty much all my TV viewing on DVD or Blu-Ray, so I won't see the Deadwood movie until it's released in one of those formats, but of course I'm greatly looking forward to it (I had vain hopes that it would get at least a cursory theatrical release; it would have merited another trek to Torrance if need be).
I never watched Lovejoy, and I remember it mostly because it used to be referenced on MST3K. Until Sexy Beast, I mostly thought of McShane as one of the suspects from my beloved The Last of Sheila.(I believe he was the E in SHEILA)
Seriously, McShane as Al is a performance and a character for the ages. The first season finale is full of amazing Al moments (such as the resolution of the dying Reverend storyline).
I forgot I have the London cast album of the stage musical The Witches of Eastwick, with McShane in the Nicholson role. I've had it so long that I must have actually played it, but I don't remember any of it.
He seems like a good choice for the part, but don't know if he can sing or just Rex Harrisoned his way through it.