Personally my most recommended series to anyone. It's at the top for me all-time more-so than The Wire, GoT, True Detective S01 or Lost. It pains me when I suggest this to people and they never give it a watch. It truly hits the mark in so many categories and Ian McShane as Al Swearengen is probably the best acting I've ever encountered in a series.
The more times I rewatch it the more I appreciate characters I didn't favor in previous viewings like EB Farnum, Calamity Jane, Cy Tolliver, Seth Bullock (the one negative is I don't think they paid justice to the story of Seth Bullock even though he was the co-lead in the series and had ample screen time). The George Hearst character was slightly embellished from what I've read but that's fine he was a good antagonist. Molly Parker played a great lead actress role.
If you have hyper-tuned sensibilities and can't handle strings of cursing don't bother. That's sad words in a television series have that much impact on you and you can't appreciate the context under which they're being conveyed.
Every time I open up Hulu and looking for that hidden gem of a series under HBO, or even look at great series I have saved, I still go back and watch Deadwood. I've seen it so many times and continue to watch it when I want a dose of Ian McShane's brilliance as the amazing Al Swearengen.