Agree with punters here (and 99 per cent of the blogosphere) that this is the best American TV of the past decade, if not longer. Personally I found The Sopranos overblown in comparison, even cartoonish.
That said, as much as I'd like to reimburse David Simon et al, it feels hard paying $90 for SD dvds. However, as JLee suggests, I believe the show was shot in SD; if Blu-ray does eventually become available, it will be upsampled content (like season 1 of Mad Men). Most modern TVs / players / graphics cards can do the upsampling from dvd anyhow...