I'm 4 or 5 episodes into the 2nd season, and I believe that the show is a little overrated. Although I thoroughly enjoy the show and agree that it's still in the top tier of shows, it's not even in the conversation of "the best show of all time."
I think part of the problem is that I'm watching it AFTER watching Breaking Bad and Mad Men for the past 4 years. Had I watched it when it first came out, I may have thought it was the greatest show of all time...because it might have been back then. The only stuff you really had to compare it to back then was Law & Order and maybe The Sopranos.
If I had to rank it with all the shows that exist today, I'd probably put it somewhere around the level of Sons of Anarchy. That's a tremendous complement, but it's still not even close to Breaking Bad (which is #1 by a mile).
You also have to keep in mind that I haven't yet seen the entire body of work which I realize is necessary to properly rate the show...especially with this show apparently.
I've also found watching shows when they originally air when you have to wait an entire week before each episode makes them more interesting. The anticipation, speculation, suspense, and emotion in general are much greater when you have to wait for the next episode, especially when you get to discuss it with other fans for an entire week. When I have to wait a week, I find myself watching shows 2 or 3 times throughout that week which helps me catch things I missed and be more aware of the subtle nuances and critically analyze the show better...making me truly appreciate the show more.
Once I've finished the final season, I'll see how my opinion has changed. But as of right now, I just don't think it's in my top 10 of all time (although it's not far off).