I finished watching all three seasons of Deadwood back to back, before watching the movie last night. In short, it's a huge disappointment. There is no tying up of loose end that some reviewers claim. What it does do, is leave the door open (again) to possible future seasons or movies.
Without giving away the movie or plot as a whole, there is much left still undone, unanswered and leaving the viewing with a "that's it?!" moment when the credits roll.
Odd thing to point out - it seems all the men (and Jewell) aged, but none of the other pivotal woman in the show aged at all. Very odd.
If you were hoping this was be exclamation and ending chapter in the a groundbreaking series, sadly this is not it. Unless your just one of the Hoopleheads, and then you might think it's great.