This is without a doubt the absolute best show I have ever seen. Each season seems to take it to a whole new level. I do agree that season 2 lagged a bit, but it picked up near the end.
I was going to buy the BD sets a few months ago so that I could rewatch the entire series before the final season. It's definitely the kind of show where seeing it twice would help notice more details, and the kind of show where small details actually matter. I decided against this only because, I have already invested so many hours into the show, what if the ending sucks? I would be twice as pissed! If the end is as amazing as the rest, then I will rewatch the series, on blu-ray.
It's also much better to watch the show on BD/DVD cus it's so addictive. I would much prefer to wait, but I would inevitably hear spoilers, and that would be unacceptable.