Jay:
Excellent suggestions abound on this thread.
"Sons of Anarchy." It's an excellent production and the later seasons will feel like a "Deadwood" revival. I understand SOA is very popular in the UK.
"Boardwalk Empire" is another favorite. The production values, characters and scripting will suck you in entirely. The main character, Steve Buscemi, worked as a fireman while he made his bones in the NYC acting arena. On 9/11 he made his way to his old firehouse and, IIRC, worked seven days or so days straight assisting his crew. Up until then, I'd always thought he was just another douche-bag Indie actor/friend of Adam Sandler. He had a short character arc on "The Sopranos" - another superb, multi-year HBO series you might enjoy - and directed several episodes as well.
Buscemi is a wispy thin guy. But shame on me for thinking that he was "just" another actor. This guy is best friend, ride the river material.
"Longmire" is one of my favorite shows. (I joined Netflix two seasons ago after A&E dropped it.) I hope you've watched "Peaky Blinders" on the BBC, Jay. I put that series right up there alongside "The Sopranos" and "Boardwalk Empire."
Finally, I'll second "The Vikings." It might not be historically accurate but it's certainly better than anything we've had to date on a group of bad-ass hombres who sailed up the Seine, sacked Paris and then settled various ports of call in North America.
Fnord