The Wire is the best TV show I have ever seen. I have seen a LOT of shows, so I don't make that statement lightly. Breaking Bad is amazing too, and it's up there, along with The Shield, M.A.S.H., Seinfeld, Sopranos, etc.
I really don't think you can call yourself a serious television viewer if you haven't watched The Wire. Wish it was in HD though, but SD gives it a gritty feel.