My boyfriend and I have been a fan of Deadwood since we decided to rent the first season a couple years ago. We both love how perfectly the show depicts the behaviour, language, and political intrigues of a town just beginning to establish itself during frontier times. It's one of those rare shows that doesn't dumb down it's material for viewers. You have to pay attention to nearly every bit of dialogue and action or risk being completely lost as to what is happening.
The beautiful thing about Deadwood, though, is that it makes you truly want to pay attention to every bit of dialogue, what's occuring with each of the characters, and keep track of the complex politics of an outlaw town struggling to find it's way in a newly formed America. All three seasons of Deadwood are sheer poetry, but the last one is especially poignant. Tragically it is Deadwood's swan song, which is sad because with it's complexity of characters and storylines, it was a show that could have lasted numerous seasons. Most TV shows fade away because they've run out of stories to tell; Deadwood had only just begun to tell it's tale. It's disheartening to be a fan of an amazing show in a time when "great" TV is often decided by ratings and advertising dollars.