When it comes to blu-rays, in my mind there are two reasons to purchase: one, because it comes in a cool package with lots of extras; or two, because the picture and audio have been cleaned up and restored beyond anything previously available.
So Dexter season seven will be out on DVD and blu-ray next week - perfect timing in case you need to catch up before the eighth and final season starts on June 30th. I got a peek at the set before the release and frankly, it doesn't fit in with my two above conditions.
For starters, Dexter is new. There is nothing to be enhanced or cleaned up. Sure, it looks just a touch more crisp than the Showtime HD channel, but not much. So it looks great... it just doesn't really look noticeably better than the HD broadcast.
Then there are the extras. There aren't any. None. No deleted scenes; no commentary; no behind-the-scenes footage. They didn't even include the Dexter: Early Cuts that aired on the web before the season started. The only "bonus" is a code to download the pilot episode of Showtime's new series Ray Donovan. Even that is kind of half-assed: it is only available on UltraViolet, which I personally don't like because it requires an internet connection to watch anything on UltraViolet.
So if you are just interested in catching up or re-watching last season of Dexter, you may want to consider buying the season from iTunes or Amazon Instant. The season, in HD, is only about $35 and you get it instantly. If you prefer a hard copy, the blu-ray will run you $45 on Amazon.