Deadwood was great at the time, I think it dropped off pretty sharply in season 3, despite having one of the most brutal fight scenes in TV history.
Or at least that's how I remember it: must admit I tried to rewatch it a couple of years back and couldn't get into it again.
Lots of great characters though. Dayton Callie, Rebecca Sievert, Jim Beaver, Brad Dourif, Jeffrey Jones, William Sanderson, Garret Dillahunt, William Earl Brown are all great as second tier characters. They tend to keep showing up in good stuff too.