I think it is helpful to separate the WATCH THESE FIRST from GOOD SHOWS. Here are my short list of WATCH THESE FIRST:
The Wire
Game of Thrones
Breaking Bad
Any show that I can't recommend to everyone and anyone I took off the list. Rome was AMAZING, but it is really hard to get into if you don't watch the DVD with the popups telling you what the f*** they are talking about. There is great historical context in every scene.
Game of Thrones is probably impossible to understand without doing some research on HBO's website or reading the books, but it is so damn good, it is on my list anyway.
24 first season was also amazing, but I don't know if time will treat it well. Something is keeping me from putting it on the list, not sure what.
For western types, Hell on Wheels and Deadwood are great, but not for everyone.
And for the purpose of this thread, I am keeping comedies off the list as he was looking for a Sopranos replacement.